feat(坐标轴): 支持配置纵轴等分刻度

新增示例谐波对比数据，完善图例、多轴和演示测试，并同步文档说明。

README.md

@@ -96,37 +96,37 @@ const data = ref<WaveformData>({
 
 ### Props
 
-| Prop                              | 类型                                        | 默认值                                                  | 说明                               |
-| --------------------------------- | ------------------------------------------- | ------------------------------------------------------- | ---------------------------------- |
-| `data`                            | `WaveformData`                              | 必填                                                    | 波形数据                           |
-| `displayMode`                     | `'independent' \| 'separated' \| 'compact'` | `'independent'`                                         | 图框布局                           |
-| `overlayMode`                     | `'single-axis' \| 'multi-axis'`             | `'single-axis'`                                         | 叠加曲线的 Y 轴模式                |
-| `timeUnit`                        | `'s' \| 'ms'`                               | `'ms'`                                                  | 坐标轴和 tooltip 展示单位          |
-| `xLabel` / `yLabel`               | `string`                                    | `时间（timeUnit）` / `'幅值'`                           | 坐标轴名称                         |
-| `lineColor`                       | `string`                                    | `'#0960bd'`                                             | 单波形默认颜色                     |
-| `width` / `height`                | `number`                                    | 自适应                                                  | 组件总尺寸，单位为 CSS 像素        |
-| `zoomable` / `showTooltip`        | `boolean`                                   | `true` / `true`                                         | 缩放和数值 tooltip 开关            |
-| `pannable`                        | `boolean`                                   | `false`                                                 | 空格拖拽平移开关                   |
-| `minZoomSpan`                     | `number`                                    | 未设置                                                  | 最小缩放跨度，使用原始 X 数据单位  |
-| `minVisiblePoints`                | `number`                                    | `0`                                                     | 缩放后至少保留的不同 X 坐标数      |
+| Prop                              | 类型                                        | 默认值                                                  | 说明                                          |
+| --------------------------------- | ------------------------------------------- | ------------------------------------------------------- | --------------------------------------------- |
+| `data`                            | `WaveformData`                              | 必填                                                    | 波形数据                                      |
+| `displayMode`                     | `'independent' \| 'separated' \| 'compact'` | `'independent'`                                         | 图框布局                                      |
+| `overlayMode`                     | `'single-axis' \| 'multi-axis'`             | `'single-axis'`                                         | 叠加曲线的 Y 轴模式                           |
+| `timeUnit`                        | `'s' \| 'ms'`                               | `'ms'`                                                  | 坐标轴和 tooltip 展示单位                     |
+| `xLabel` / `yLabel`               | `string`                                    | `时间（timeUnit）` / `'幅值'`                           | 坐标轴名称                                    |
+| `lineColor`                       | `string`                                    | `'#0960bd'`                                             | 单波形默认颜色                                |
+| `width` / `height`                | `number`                                    | 自适应                                                  | 组件总尺寸，单位为 CSS 像素                   |
+| `zoomable` / `showTooltip`        | `boolean`                                   | `true` / `true`                                         | 缩放和数值 tooltip 开关                       |
+| `pannable`                        | `boolean`                                   | `false`                                                 | 空格拖拽平移开关                              |
+| `minZoomSpan`                     | `number`                                    | 未设置                                                  | 最小缩放跨度，使用原始 X 数据单位             |
+| `minVisiblePoints`                | `number`                                    | `0`                                                     | 缩放后至少保留的不同 X 坐标数                 |
 | `initialXDomain`                  | `[number, number]`                          | 未设置                                                  | 所有图框的初始 X 范围（可超出数据，空白显示） |
 | `initialXDomains`                 | `Record<string, [number, number]>`          | 未设置                                                  | 按 track/series ID 配置初始范围（可超出数据） |
-| `xDomainStrategy`                 | `WaveformXDomainStrategy`                   | `{ type: 'data' }`                                      | 自动 X 轴视口范围策略              |
-| `yDomain`                         | `[number, number]`                          | 未设置                                                  | 所有波形的固定 Y 轴范围            |
-| `yDomains`                        | `Record<string, [number, number]>`          | 未设置                                                  | 按 track/series ID 配置固定范围    |
-| `grid`                            | `WaveformGridOptions`                       | `{ rowCount: 2, columnCount: 1, showPagination: true }` | 网格和分页                         |
-| `axes`                            | `WaveformAxesOptions`                       | 轴线均显示                                              | X/Y 轴基线显隐与 X 轴 label 格式化 |
-| `rendering`                       | `WaveformRenderingOptions`                  | `{}`                                                    | 降采样与点/误差棒间距              |
-| `title` / `legend` / `frameStyle` | 对应公开类型                                | 未设置                                                  | 标题、图例和图框样式               |
-| `frameNumber`                     | `string \| number`                          | 未设置                                                  | 图框水印内容                       |
-| `zeroLine`                        | `WaveformZeroLineOptions`                   | `{ visible: false }`                                    | 零值参考线显隐与样式               |
-| `cleanView`                       | `boolean`                                   | `false`                                                 | 保留波形、图框和刻度的净图模式     |
-| `presentationMode`                | `boolean`                                   | `false`                                                 | 禁用绘图区交互的展示模式           |
-| `annotations`                     | `WaveformAnnotation[]`                      | `[]`                                                    | 受控标注数据                       |
-| `annotationsVisible`              | `boolean`                                   | `true`                                                  | 标注图层显隐                       |
-| `interactionMode`                 | `'zoom' \| 'annotation'`                    | `'zoom'`                                                | 左键交互模式                       |
-| `hiddenSeriesIds`                 | `string[]`                                  | 未设置                                                  | 受控隐藏系列 ID                    |
-| `defaultHiddenSeriesIds`          | `string[]`                                  | `[]`                                                    | 非受控模式的初始隐藏系列           |
+| `xDomainStrategy`                 | `WaveformXDomainStrategy`                   | `{ type: 'data' }`                                      | 自动 X 轴视口范围策略                         |
+| `yDomain`                         | `[number, number]`                          | 未设置                                                  | 所有波形的固定 Y 轴范围                       |
+| `yDomains`                        | `Record<string, [number, number]>`          | 未设置                                                  | 按 track/series ID 配置固定范围               |
+| `grid`                            | `WaveformGridOptions`                       | `{ rowCount: 2, columnCount: 1, showPagination: true }` | 网格和分页                                    |
+| `axes`                            | `WaveformAxesOptions`                       | 轴线均显示                                              | X/Y 轴基线、Y 轴分割数与 X 轴 label 格式化    |
+| `rendering`                       | `WaveformRenderingOptions`                  | `{}`                                                    | 降采样与点/误差棒间距                         |
+| `title` / `legend` / `frameStyle` | 对应公开类型                                | 未设置                                                  | 标题、图例和图框样式                          |
+| `frameNumber`                     | `string \| number`                          | 未设置                                                  | 图框水印内容                                  |
+| `zeroLine`                        | `WaveformZeroLineOptions`                   | `{ visible: false }`                                    | 零值参考线显隐与样式                          |
+| `cleanView`                       | `boolean`                                   | `false`                                                 | 保留波形、图框和刻度的净图模式                |
+| `presentationMode`                | `boolean`                                   | `false`                                                 | 禁用绘图区交互的展示模式                      |
+| `annotations`                     | `WaveformAnnotation[]`                      | `[]`                                                    | 受控标注数据                                  |
+| `annotationsVisible`              | `boolean`                                   | `true`                                                  | 标注图层显隐                                  |
+| `interactionMode`                 | `'zoom' \| 'annotation'`                    | `'zoom'`                                                | 左键交互模式                                  |
+| `hiddenSeriesIds`                 | `string[]`                                  | 未设置                                                  | 受控隐藏系列 ID                               |
+| `defaultHiddenSeriesIds`          | `string[]`                                  | `[]`                                                    | 非受控模式的初始隐藏系列                      |
 
 所有公开类型均可从包入口导入，例如 `WaveformData`、`WaveformSeries`、
 `WaveformAnnotation`、`WaveformLineStyle`、`WaveformRenderingOptions`、
@@ -208,7 +208,8 @@ import 'waveform-analysis/style.css'
 
 范围优先级为 `trackId` 配置、`seriesId` 配置、全局 `yDomain`、数据自动范围。上下限必须
 是两个有限且不相等的数字；倒序范围会自动调整为升序，无效配置会回退到下一优先级。
-固定范围会精确作为坐标域使用，不会经过 D3 的 `nice()` 扩展。
+固定范围作为 Y 轴刻度算法的初始范围；轴会按漂亮步长经过 D3 的 `nice()` 扩展，确保主刻度
+等间距。原始数据和传入的范围值不会被修改。
 
 单值轴叠加模式会合并同一根轴上所有可见系列的有效范围；多值轴模式按系列分别使用配置，
 超过四根轴后复用第 4 根轴的系列会取范围并集。隐藏系列不参与公共范围合并。
@@ -216,6 +217,16 @@ import 'waveform-analysis/style.css'
 固定范围存在时，对应图框的 Y 轴不会被平移或视口重置覆盖；X 轴缩放、平移和重置保持原有
 行为。运行时更新或移除 `yDomain` / `yDomains` 会立即重新布局，移除后恢复自动范围。
 
+### Y 轴自动等分
+
+Y 轴默认显示 5 个主刻度（包含上下端点），并使用类似 ECharts 的 `1 / 2 / 5 × 10ⁿ` 漂亮
+步长，保证主刻度之间数值等间距。可以通过 `axes.y.splitNumber` 指定主刻度总数；每条
+Y 轴会独立计算：
+
+```vue
+<WaveformChart :data="chartData" :axes="{ y: { splitNumber: 5 } }" />
+```
+
 ### 缩放后按可视区间加载数据
 
 组件支持 Plotly 风格的矩形框选缩放：在 zoom 模式下按住鼠标左键拖拽，松开后同时缩放
@@ -253,6 +264,20 @@ X 轴且包含多个轨道时使用按稳定 track ID 索引的 `yRanges`。平
 重置组件内部缩放并触发 `zoom-reset`；调用方应在事件中取消区间请求并恢复首次完整数据。
 外部重置按钮也可以通过模板引用调用组件公开的 `resetViewport()` 方法，然后执行相同的数据恢复逻辑。
 
+宿主在替换局部数据后如果需要恢复之前保存的 X 视口，可以调用公开的
+`setViewportDomain(domain, trackIndex?)`。传入范围使用原始秒坐标，组件会按当前数据边界、
+`xDomainStrategy`、`minZoomSpan` 和 `minVisiblePoints` 重新约束；无效范围会被忽略。共享
+X 轴模式直接传入一个范围，独立模式可以按实际 `trackIndex` 分别设置（省略 `trackIndex`
+时应用到当前所有图框）：
+
+```ts
+chartRef.value?.setViewportDomain(previousDomain)
+chartRef.value?.setViewportDomain(trackDomain, trackIndex)
+```
+
+建议在 `data` 引用更新后调用该方法。组件也会在数据引用变更时重投影当前内部视口，避免新
+数据边界使旧 transform 失效；`resetViewport(trackIndex?)` 的既有行为保持不变。
+
 没有显式配置初始范围时，可以通过 `xDomainStrategy` 将数据范围扩展为便于阅读的视口端点。
 默认的 `{ type: 'data' }` 保持数据最小值和最大值不变；`type: 'nice'` 使用固定刻度数量计算
 易读边界，且只扩展视口，不修改原始点位、tooltip、标注或缩放事件值：
@@ -284,6 +309,34 @@ X 轴且包含多个轨道时使用按稳定 track ID 索引的 `yRanges`。平
 Tooltip 每个系列按 `炮号：通道  (x:值 y:值)` 格式显示。`WaveformSeries.shotNo` 为空或未提供时，
 炮号显示为“未配置炮号”；Tooltip 不显示单位和误差附加文本。
 
+### 纵轴单位
+
+可在每个 `WaveformSeries` 上设置可选的 `unit`，单位会显示在对应 Y 轴的顶部刻度中：
+
+```ts
+const chartData = {
+  kind: 'series',
+  series: [
+    {
+      id: 'voltage',
+      name: '电压',
+      unit: 'V',
+      data: {
+        kind: 'points',
+        points: [
+          { x: 0, y: 1200 },
+          { x: 1, y: 3000 },
+        ],
+      },
+    },
+  ],
+} satisfies WaveformData
+```
+
+当 Y 轴使用科学计数法时，顶部刻度格式为 `E+03 (V) 3`；未使用科学计数法时，格式为
+`(V) 3`。单位为空、全为空白或未配置时，不显示 `(单位)`，例如仍显示为 `E+03 3` 或 `3`。
+多 Y 轴模式下，每根轴使用该轴首个 series 的单位。
+
 ### 线型、点型与误差棒
 
 每条序列可以独立设置连线方式、数据点符号和误差棒：
@@ -415,7 +468,8 @@ Demo 左侧控制面板提供标题实时预览，可配置标题名称、显隐
 
 ### 图例与曲线显隐
 
-`legend.backgroundColor` 设置多曲线图例的背景颜色。该字段接受任意有效 CSS 颜色值，
+每个图框独立管理自己的图例：图框内有两条或更多曲线时显示图例，只有一条曲线时不显示。
+`legend.backgroundColor` 设置图例的背景颜色。该字段接受任意有效 CSS 颜色值，
 可通过 `rgba(...)` 或 `hsla(...)` 中的 alpha 通道调整透明度：
 
 ```vue
@@ -654,7 +708,7 @@ async function importAnnotationFile(file: File) {
 字段无效时会抛出 `TypeError`，不会返回部分结果。导入包含未知 `seriesId` 的标注是允许的，
 对应曲线加载后会恢复显示。文件选择、错误提示和下载由业务层实现。
 
-X 轴刻度和左右端点先按 `timeUnit` 转换为秒或毫秒，再显示为不带分组符和科学计数法的完整普通十进制值，并可通过 `axes.x.labelFormatter` 自定义。Y 轴会根据完整显示域选择格式：最大绝对值在 `[0.01, 100)` 时显示两位普通小数；大于等于 `100`，或大于 `0` 且小于 `0.01` 时，刻度显示两位缩放值，并在轴末端单独显示共享倍率 `E±NN`，多 Y 轴分别计算倍率。tooltip 使用最多 4 位小数的本地化普通数字并省略无意义尾零；标注编辑器的 X 坐标跟随 `timeUnit` 并固定 3 位小数，Y 坐标显示完整普通十进制。所有格式化都只发生在展示层，内部坐标值保持原始精度。
+X 轴刻度和左右端点先按 `timeUnit` 转换为秒或毫秒，再显示为不带分组符和科学计数法的完整普通十进制值，并可通过 `axes.x.labelFormatter` 自定义。Y 轴会根据完整显示域选择格式：最大绝对值在 `[0.01, 100)` 时显示两位普通小数；大于等于 `100`，或大于 `0` 且小于 `0.01` 时，刻度显示两位缩放值，并在顶部刻度单独显示共享倍率 `E±NN`。如果 series 配置了 `unit`，顶部刻度会在倍率后追加 `(单位)`；没有科学计数法时也会显示 `(单位)`，多 Y 轴分别使用对应轴首个 series 的单位。tooltip 使用最多 4 位小数的本地化普通数字并省略无意义尾零；标注编辑器的 X 坐标跟随 `timeUnit` 并固定 3 位小数，Y 坐标显示完整普通十进制。所有格式化都只发生在展示层，内部坐标值保持原始精度。
 标注框默认布局在采样点正上方，只做绘图区边界裁剪；文本框通过连接箭头指向标注位置，多个标注重叠时可通过拖动手动避让。
 
 ## 事件

package.json

@@ -1,6 +1,6 @@
 {
   "name": "waveform-analysis",
-  "version": "0.1.37",
+  "version": "0.1.41",
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/types/index.d.ts",

src/App.test.ts

@@ -235,7 +235,7 @@ describe('App workspace layout', { timeout: 20_000 }, () => {
       tracks.map((track) =>
         track.findAll('.waveform-chart__series').map((item) => item.attributes('data-series-name')),
       ),
-    ).toEqual([['正弦基波'], ['谐波扰动'], ['阻尼振荡'], ['阶跃响应']])
+    ).toEqual([['正弦基波'], ['谐波扰动', '谐波对比'], ['阻尼振荡'], ['阶跃响应']])
     expect(
       tracks
         .slice(1)
@@ -253,6 +253,7 @@ describe('App workspace layout', { timeout: 20_000 }, () => {
     expect(simulatedSeries.map((item) => item.name)).toEqual([
       '正弦基波',
       '谐波扰动',
+      '谐波对比',
       '阻尼振荡',
       '阶跃响应',
       '脉冲响应',
@@ -321,7 +322,6 @@ describe('App workspace layout', { timeout: 20_000 }, () => {
     const styleSelect = frameControls.findAllComponents(Select)[0]
 
     expect(colorPickers).toHaveLength(2)
-
     const initialFrames = wrapper.findAll('.waveform-chart__plot-frame')
     expect(initialFrames.length > 1 && initialFrames.every((frame) => frame.attributes('stroke-width') === '2')).toBe(true)
 

src/components/WaveformChart.vue

@@ -36,6 +36,7 @@ const controller = useWaveformChartController(props as ResolvedWaveformChartProp
 
 defineExpose({
   resetViewport: controller.resetViewport,
+  setViewportDomain: controller.setViewportDomain,
 })
 </script>
 

src/components/core/fixedYDomainLayout.test.ts

@@ -35,7 +35,7 @@ function track(seriesList: DisplaySeries[]): DisplayTrack {
 }
 
 describe('fixed Y-domain layout', () => {
-  it('uses an exact global fixed domain without applying nice bounds', () => {
+  it('expands a global fixed domain to nice equal intervals', () => {
     const sourceTrack = track([series('a', 0, 100)])
     const result = buildTrackLayouts({
       cells: [
@@ -66,10 +66,80 @@ describe('fixed Y-domain layout', () => {
       showCompactEmptyTracks: false,
     })[0]
 
-    expect(result?.yScale.domain()).toEqual([3, 97])
-    expect(result?.yAxes[0]?.tickValues).toContain(3)
-    expect(result?.yAxes[0]?.tickValues).toContain(97)
-    expect(result?.seriesPaths[0]?.yScale.domain()).toEqual([3, 97])
+    expect(result?.yScale.domain()).toEqual([0, 100])
+    expect(result?.yAxes[0]?.tickValues).toContain(0)
+    expect(result?.yAxes[0]?.tickValues).toContain(100)
+    expect(result?.seriesPaths[0]?.yScale.domain()).toEqual([0, 100])
+  })
+
+  it('uses the configured split number for fixed domains', () => {
+    const result = buildTrackLayouts({
+      cells: [
+        {
+          slotIndex: 0,
+          row: 0,
+          column: 0,
+          left: 0,
+          top: 0,
+          width: 120,
+          height: 100,
+          plotHeight: 100,
+          cellHeight: 130,
+          xAxisBand: 30,
+          series: track([series('a', 0, 100)]),
+        },
+      ],
+      grid: { rowCount: 1, columnCount: 1, showPagination: false, trackLines: {} },
+      displayMode: 'independent',
+      overlayMode: 'single-axis',
+      independentTransforms: [zoomIdentity],
+      sharedZoomDomain: [0, 1],
+      fixedYDomain: [3, 97],
+      yAxisSplitNumber: 5,
+      timeUnit: 'ms',
+      rendering: DEFAULT_WAVEFORM_RENDERING_OPTIONS,
+      hideSecondaryLabels: false,
+      yAxisLabelX: -50,
+      showCompactEmptyTracks: false,
+    })[0]
+
+    expect(result?.yAxes[0]?.majorTicks).toEqual([0, 25, 50, 75, 100])
+  })
+
+  it('defaults to five ticks and supports a two-tick axis', () => {
+    const build = (splitNumber?: number) =>
+      buildTrackLayouts({
+        cells: [
+          {
+            slotIndex: 0,
+            row: 0,
+            column: 0,
+            left: 0,
+            top: 0,
+            width: 120,
+            height: 100,
+            plotHeight: 100,
+            cellHeight: 130,
+            xAxisBand: 30,
+            series: track([series('a', 3, 97)]),
+          },
+        ],
+        grid: { rowCount: 1, columnCount: 1, showPagination: false, trackLines: {} },
+        displayMode: 'independent',
+        overlayMode: 'single-axis',
+        independentTransforms: [zoomIdentity],
+        sharedZoomDomain: [0, 1],
+        fixedYDomain: [3, 97],
+        yAxisSplitNumber: splitNumber,
+        timeUnit: 'ms',
+        rendering: DEFAULT_WAVEFORM_RENDERING_OPTIONS,
+        hideSecondaryLabels: false,
+        yAxisLabelX: -50,
+        showCompactEmptyTracks: false,
+      })[0]?.yAxes[0]?.majorTicks
+
+    expect(build()).toHaveLength(5)
+    expect(build(2)).toEqual([0, 100])
   })
 
   it('resolves track, series, and global fixed-domain precedence', () => {

src/components/core/layout.test.ts

@@ -9,6 +9,7 @@ import {
   findClosestTrackAtPointer,
   MAX_MULTI_Y_AXIS_COUNT,
   measureYAxisGroupClearance,
+  resolveYAxisTickCount,
 } from './layout'
 
 function series(id: string, minimum: number, maximum: number): DisplaySeries {
@@ -119,8 +120,15 @@ describe('multi-value Y-axis grouping', () => {
       showCompactEmptyTracks: false,
     })[0]
 
-    expect(result?.yScale.domain()).toEqual([25, 75])
-    expect(result?.seriesPaths[0]?.yScale.domain()).toEqual([25, 75])
+    expect(result?.yScale.domain()).toEqual([20, 80])
+    expect(result?.seriesPaths[0]?.yScale.domain()).toEqual([20, 80])
+  })
+
+  it('normalizes configured Y-axis split counts', () => {
+    expect(resolveYAxisTickCount(100, 0)).toBe(2)
+    expect(resolveYAxisTickCount(100, 4.8)).toBe(4)
+    expect(resolveYAxisTickCount(100, Number.NaN)).toBe(5)
+    expect(resolveYAxisTickCount(220)).toBe(5)
   })
 
   it('keeps every overlaid series on one axis in single-axis mode', () => {

src/components/core/layout.ts

@@ -20,6 +20,13 @@ const Y_AXIS_OUTER_PADDING = 4
 const Y_AXIS_LABEL_GAP = 6
 const Y_AXIS_LABEL_BAND_WIDTH = 24
 
+export function resolveYAxisTickCount(_plotHeight: number, splitNumber?: number): number {
+  if (typeof splitNumber === 'number' && Number.isFinite(splitNumber)) {
+    return Math.max(2, Math.floor(splitNumber))
+  }
+  return 5
+}
+
 export interface YAxisSeriesGroup {
   index: number
   side: 'left' | 'right'
@@ -103,16 +110,22 @@ export function axisTextMetrics(
   domain: [number, number],
   nice = true,
   tickValues?: number[],
+  unit?: string,
+  tickCount = 10,
 ): { tickTextWidth: number } {
+  const effectiveTickCount =
+    typeof tickCount === 'number' && Number.isFinite(tickCount)
+      ? Math.max(2, Math.floor(tickCount))
+      : 10
   const scale = scaleLinear(domain, [1, 0])
-  if (nice) scale.nice()
+  if (nice) scale.nice(effectiveTickCount)
   const [axisMin, axisMax] = scale.domain()
-  const values = tickValues ?? Array.from(new Set([axisMin, ...scale.ticks(10), axisMax]))
+  const values = tickValues ?? scale.ticks(effectiveTickCount)
   const topTickValue = Math.max(...values)
   const maximumTickCharacters = Math.max(
     1,
     ...values.map(
-      (value) => formatScientificAxisLabel(value, { axisMin, axisMax, topTickValue }).length,
+      (value) => formatScientificAxisLabel(value, { axisMin, axisMax, topTickValue, unit }).length,
     ),
   )
   return {
@@ -120,9 +133,10 @@ export function axisTextMetrics(
   }
 }
 
-export function measureYAxisGroupClearance(group: YAxisSeriesGroup): number {
+export function measureYAxisGroupClearance(group: YAxisSeriesGroup, tickCount?: number): number {
   return (
-    axisTextMetrics(group.domain, !group.fixed).tickTextWidth +
+    axisTextMetrics(group.domain, true, undefined, group.seriesList[0]?.unit, tickCount)
+      .tickTextWidth +
     Y_AXIS_TICK_PADDING +
     Y_AXIS_LABEL_GAP +
     Y_AXIS_LABEL_BAND_WIDTH +
@@ -130,9 +144,10 @@ export function measureYAxisGroupClearance(group: YAxisSeriesGroup): number {
   )
 }
 
-function measureYAxisGroupTickClearance(group: YAxisSeriesGroup): number {
+function measureYAxisGroupTickClearance(group: YAxisSeriesGroup, tickCount?: number): number {
   return (
-    axisTextMetrics(group.domain, !group.fixed).tickTextWidth +
+    axisTextMetrics(group.domain, true, undefined, group.seriesList[0]?.unit, tickCount)
+      .tickTextWidth +
     Y_AXIS_TICK_PADDING +
     Y_AXIS_OUTER_PADDING
   )
@@ -143,13 +158,14 @@ export function measureTrackYAxisClearance(
   overlayMode: WaveformOverlayMode,
   yDomain?: WaveformYDomain,
   yDomains?: Record<string, WaveformYDomain>,
+  tickCount?: number,
 ): { left: number; right: number } {
   return resolveYAxisSeriesGroups(track, overlayMode, yDomain, yDomains).reduce(
     (clearance, group) => {
       clearance[group.side] +=
         overlayMode === 'multi-axis' || track.visibleSeries.length === 1
-          ? measureYAxisGroupClearance(group)
-          : measureYAxisGroupTickClearance(group)
+          ? measureYAxisGroupClearance(group, tickCount)
+          : measureYAxisGroupTickClearance(group, tickCount)
       return clearance
     },
     { left: 0, right: 0 },

src/components/core/trackLayoutBuilder.ts

@@ -25,7 +25,7 @@ import {
   type GridCellGeometry,
   type NormalizedWaveformGridOptions,
 } from './grid'
-import { axisTextMetrics, resolveYAxisSeriesGroups } from './layout'
+import { axisTextMetrics, resolveYAxisSeriesGroups, resolveYAxisTickCount } from './layout'
 import type { DisplaySeries, DisplayTrack, TrackLayout, WaveformYAxisLayout } from './types'
 import { applyXDomainStrategy } from './xDomain'
 import {
@@ -54,6 +54,7 @@ export interface BuildTrackLayoutsOptions {
   yDomains?: Record<string, [number, number]>
   timeUnit: 's' | 'ms'
   xAxisLabelFormatter?: WaveformXAxisLabelFormatter
+  yAxisSplitNumber?: number
   rendering: ResolvedWaveformRenderingOptions
   hideSecondaryLabels: boolean
   yAxisLabelX: number
@@ -124,18 +125,27 @@ export function buildTrackLayouts(options: BuildTrackLayoutsOptions): TrackLayou
     )
     const sideOffsets = { left: 0, right: 0 }
     const yAxes: WaveformYAxisLayout[] = yAxisGroups.map((group) => {
+      const tickCount = resolveYAxisTickCount(cell.plotHeight, options.yAxisSplitNumber)
+      const niceCount = Math.max(1, tickCount - 1)
       const scale = scaleLinear(group.domain, [cell.plotHeight, 0])
-      if (!group.fixed) scale.nice()
-      const majorTicks = scale.ticks(Math.max(2, Math.floor(cell.plotHeight / 55)))
+      scale.nice(niceCount)
       const [axisStart, axisEnd] = scale.domain()
+      const majorTicks = Array.from(
+        { length: tickCount },
+        (_, index) => axisStart + ((axisEnd - axisStart) * index) / (tickCount - 1),
+      )
       const showAxisEnd = options.displayMode !== 'compact' || cell.row === 0
       const visibleMajorTicks = showAxisEnd
         ? majorTicks
         : majorTicks.filter((tick) => tick !== axisEnd)
-      const tickValues = Array.from(
-        new Set([axisStart, ...visibleMajorTicks, ...(showAxisEnd ? [axisEnd] : [])]),
+      const tickValues = visibleMajorTicks
+      const { tickTextWidth } = axisTextMetrics(
+        scale.domain() as [number, number],
+        false,
+        tickValues,
+        group.seriesList[0]?.unit,
+        tickCount,
       )
-      const { tickTextWidth } = axisTextMetrics(group.domain, !group.fixed, tickValues)
       const clearance =
         tickTextWidth +
         Y_AXIS_TICK_PADDING +

src/components/core/useWaveformChartController.ts

@@ -259,6 +259,9 @@ export function useWaveformChartController(
     trackLayouts,
     innerWidth,
     innerHeight,
+    sharedZoomDomain,
+    initialXDomain,
+    sharedTransform,
     activeInteractionMode,
     hiddenSeriesIdSet,
     internalHiddenSeriesIds,

src/components/core/useWaveformChartLifecycle.ts

@@ -39,6 +39,9 @@ interface LifecycleContext {
   trackLayouts: ComputedRef<TrackLayout[]>
   innerWidth: ComputedRef<number>
   innerHeight: ComputedRef<number>
+  sharedZoomDomain: ComputedRef<[number, number]>
+  initialXDomain: ComputedRef<[number, number]>
+  sharedTransform: ShallowRef<ZoomTransform>
   activeInteractionMode: ComputedRef<string | undefined>
   hiddenSeriesIdSet: ComputedRef<Set<string>>
   internalHiddenSeriesIds: Ref<Set<string>>
@@ -93,6 +96,9 @@ export function useWaveformChartLifecycle(context: LifecycleContext) {
     trackLayouts,
     innerWidth,
     innerHeight,
+    sharedZoomDomain,
+    initialXDomain,
+    sharedTransform,
     activeInteractionMode,
     hiddenSeriesIdSet,
     internalHiddenSeriesIds,
@@ -144,25 +150,24 @@ export function useWaveformChartLifecycle(context: LifecycleContext) {
     emit('page-change', nextPage, pageCount.value)
   }
 
+  let pendingSharedXDomain: [number, number] | undefined
   let pendingIndependentXDomains: Array<[number, number] | undefined> | undefined
 
   function handleBeforeDataReferenceChange() {
-    if (props.displayMode !== 'independent') return
-    pendingIndependentXDomains = trackLayouts.value.map((track) => {
-      const configuredDomain =
-        props.initialXDomains?.[track.series.trackId ?? track.series.id] ??
-        props.initialXDomains?.[track.series.id] ??
-        props.initialXDomain
-      if (
-        !configuredDomain ||
-        !Number.isFinite(configuredDomain[0]) ||
-        !Number.isFinite(configuredDomain[1]) ||
-        configuredDomain[0] === configuredDomain[1]
-      ) {
-        return undefined
-      }
-      return track.xScale.domain() as [number, number]
-    })
+    if (props.displayMode === 'independent') {
+      pendingSharedXDomain = undefined
+      pendingIndependentXDomains = trackLayouts.value.map((track) => {
+        const current = track.xScale.domain() as [number, number]
+        const boundary = resolveInitialTrackDomain(track)
+        return current[1] - current[0] < boundary[1] - boundary[0] - 1e-12 ? current : undefined
+      })
+      return
+    }
+    pendingIndependentXDomains = undefined
+    const current = sharedZoomDomain.value
+    const boundary = initialXDomain.value
+    pendingSharedXDomain =
+      current[1] - current[0] < boundary[1] - boundary[0] - 1e-12 ? [...current] : undefined
   }
 
   function handleDataReferenceChange() {
@@ -186,10 +191,15 @@ export function useWaveformChartLifecycle(context: LifecycleContext) {
         })
         independentTransforms.value = nextTransforms
         pendingIndependentXDomains = undefined
-        void nextTick(configureZoom)
-        return
+      } else if (props.displayMode !== 'independent' && pendingSharedXDomain) {
+        const boundary = initialXDomain.value
+        const groups = trackLayouts.value
+          .filter((track) => track.hasVisibleSeries)
+          .map((track) => track.seriesList)
+        const domain = constrainZoomDomain(pendingSharedXDomain, boundary, groups, props)
+        sharedTransform.value = transformForDomain(domain, boundary, innerWidth.value)
+        pendingSharedXDomain = undefined
       }
-      pendingIndependentXDomains = undefined
       configureZoom()
     })
   }

src/components/core/useWaveformLayout.ts

@@ -112,7 +112,16 @@ export function useWaveformLayout(context: LayoutContext) {
       .flatMap((track) =>
         resolveYAxisSeriesGroups(track, props.overlayMode, props.yDomain, props.yDomains),
       )
-      .map((group) => axisTextMetrics(group.domain, !group.fixed).tickTextWidth)
+      .map(
+        (group) =>
+          axisTextMetrics(
+            group.domain,
+            true,
+            undefined,
+            group.seriesList[0]?.unit,
+            props.axes?.y?.splitNumber,
+          ).tickTextWidth,
+      )
     const tickTextWidth = Math.max(Y_AXIS_CHARACTER_WIDTH, ...axisText)
     const tickClearance = tickTextWidth + Y_AXIS_TICK_PADDING + Y_AXIS_OUTER_PADDING
     const labelCenterX = -(
@@ -157,6 +166,7 @@ export function useWaveformLayout(context: LayoutContext) {
           props.overlayMode,
           props.yDomain,
           props.yDomains,
+          props.axes?.y?.splitNumber,
         )
         return {
           left: Math.max(maximum.left, clearance.left),
@@ -298,6 +308,7 @@ export function useWaveformLayout(context: LayoutContext) {
           : sharedYDomains.value,
       timeUnit: props.timeUnit,
       xAxisLabelFormatter: props.axes?.x?.labelFormatter,
+      yAxisSplitNumber: props.axes?.y?.splitNumber,
       rendering: renderingOptions.value,
       hideSecondaryLabels: isCleanView.value || yAxisLayout.value.hideSecondaryLabels,
       yAxisLabelX: yAxisMetrics.value.labelCenterX,

src/components/interaction/useWaveformViewport.ts

@@ -11,6 +11,7 @@ import type {
 import type { AnnotationSeriesCandidate } from '../annotation'
 import { tryReleasePointerCapture } from './pointerCapture'
 import { transitionViewportInteraction } from './viewportInteractionState'
+import { createViewportDomainSetter } from './viewportDomain'
 import { constrainZoomDomain, transformForDomain } from './zoomConstraints'
 interface ViewportContext {
   props: ResolvedWaveformChartProps
@@ -344,6 +345,20 @@ export function useWaveformViewport(context: ViewportContext) {
     editorSeriesOptions.value = []
     void nextTick(configureZoom)
   }
+  const setViewportDomain = createViewportDomainSetter({
+    props,
+    trackLayouts,
+    initialXDomain,
+    resolveInitialTrackDomain,
+    innerWidth,
+    sharedTransform,
+    independentTransforms,
+    cancelPendingZoom,
+    cancelViewportDrag,
+    clearHover,
+    editorSeriesOptions,
+    configureZoom,
+  })
   const requestViewportReset = (event: MouseEvent) => {
     if (isPresentationMode.value || !props.zoomable || !isZoomMode.value) return
     if (props.displayMode === 'independent') {
@@ -372,6 +387,7 @@ export function useWaveformViewport(context: ViewportContext) {
     finishViewportDrag,
     cancelViewportDrag,
     resetViewport,
+    setViewportDomain,
     requestViewportReset,
   }
 }

src/components/interaction/viewportDomain.ts

@@ -0,0 +1,60 @@
+import { nextTick, type ComputedRef, type Ref, type ShallowRef } from 'vue'
+import type { ZoomTransform } from 'd3'
+
+import type { TrackLayout } from '../core/types'
+import type { ResolvedWaveformChartProps } from '../core/waveformChartTypes'
+import type { AnnotationSeriesCandidate } from '../annotation'
+import { constrainZoomDomain, transformForDomain } from './zoomConstraints'
+
+interface ViewportDomainContext {
+  props: ResolvedWaveformChartProps
+  trackLayouts: ComputedRef<TrackLayout[]>
+  initialXDomain: ComputedRef<[number, number]>
+  resolveInitialTrackDomain: (track: TrackLayout) => [number, number]
+  innerWidth: ComputedRef<number>
+  sharedTransform: ShallowRef<ZoomTransform>
+  independentTransforms: ShallowRef<ZoomTransform[]>
+  cancelPendingZoom: () => void
+  cancelViewportDrag: () => void
+  clearHover: () => void
+  editorSeriesOptions: Ref<AnnotationSeriesCandidate[]>
+  configureZoom: () => void
+}
+
+export function createViewportDomainSetter(context: ViewportDomainContext) {
+  return (domain: [number, number], trackIndex?: number) => {
+    if (!Number.isFinite(domain[0]) || !Number.isFinite(domain[1]) || domain[0] === domain[1])
+      return
+    context.cancelPendingZoom()
+    context.cancelViewportDrag()
+    if (context.props.displayMode === 'independent') {
+      const indexes =
+        trackIndex === undefined
+          ? context.trackLayouts.value.map((track) => track.index)
+          : [trackIndex]
+      const nextTransforms = [...context.independentTransforms.value]
+      indexes.forEach((index) => {
+        const track = context.trackLayouts.value.find((item) => item.index === index)
+        if (!track) return
+        const boundary = context.resolveInitialTrackDomain(track)
+        const constrained = constrainZoomDomain(domain, boundary, [track.seriesList], context.props)
+        nextTransforms[index] = transformForDomain(constrained, boundary, track.width)
+      })
+      context.independentTransforms.value = nextTransforms
+    } else {
+      const boundary = context.initialXDomain.value
+      const groups = context.trackLayouts.value
+        .filter((track) => track.hasVisibleSeries)
+        .map((track) => track.seriesList)
+      const constrained = constrainZoomDomain(domain, boundary, groups, context.props)
+      context.sharedTransform.value = transformForDomain(
+        constrained,
+        boundary,
+        context.innerWidth.value,
+      )
+    }
+    context.clearHover()
+    context.editorSeriesOptions.value = []
+    void nextTick(context.configureZoom)
+  }
+}

src/components/rendering/WaveformTrackAxes.vue

@@ -44,9 +44,10 @@ function renderAxes() {
     if (!element) return
     const [axisMin, axisMax] = axis.scale.domain()
     const topTickValue = Math.max(...axis.tickValues)
+    const unit = axis.seriesList[0]?.unit
     const yAxis = (axis.side === 'left' ? axisLeft(axis.scale) : axisRight(axis.scale))
       .tickFormat((value) =>
-        formatScientificAxisLabel(Number(value), { axisMin, axisMax, topTickValue }),
+        formatScientificAxisLabel(Number(value), { axisMin, axisMax, topTickValue, unit }),
       )
       .tickSize(-4)
       .tickPadding(7)

src/components/waveformChartCases/compactAndSharedHover.test.ts

@@ -65,9 +65,9 @@ describe('WaveformChart', () => {
     )
 
     expect(endTicks[0]).toHaveLength(1)
-    expect(Number(endTicks[0][0].text())).toBe(0.9)
+    expect(Number(endTicks[0][0].text())).toBe(1)
     expect(endTicks[1]).toHaveLength(1)
-    expect(Number(endTicks[1][0].text())).toBe(1.9)
+    expect(Number(endTicks[1][0].text())).toBe(2)
     expect(endTicks[2]).toHaveLength(0)
     expect(endTicks[3]).toHaveLength(0)
   })

src/components/waveformChartCases/dataLifecycle.test.ts

@@ -158,6 +158,12 @@ describe('WaveformChart', () => {
     expect(paths[0].attributes('data-series-name')).toBe('BT2_2M')
     const yAxisLabels = wrapper.findAll('.waveform-chart__y-axis-label')
     expect(yAxisLabels.map((label) => label.text())).toEqual(['BT2_2M', 'BT1_2M'])
+    expect(
+      wrapper
+        .findAll('.waveform-chart__axis--y .tick text')
+        .map((label) => label.text())
+        .some((label) => label.includes('(T)')),
+    ).toBe(true)
     expect(yAxisLabels.map((label) => label.attributes('fill'))).toEqual(['#0960bd', '#ff7f0e'])
     const labelX = Number(
       yAxisLabels[0].attributes('transform')?.match(/^translate\(([-\d.]+),/)?.[1],
@@ -255,7 +261,7 @@ describe('WaveformChart', () => {
       })
 
       expect(startTicks).toHaveLength(1)
-      expect(Number(startTicks[0].text())).toBe(0.1)
+      expect(Number(startTicks[0].text())).toBe(0)
     },
   )
 
@@ -291,7 +297,7 @@ describe('WaveformChart', () => {
         { displayMode },
       )
 
-      const expectedEndValues = [0.9, 4.9]
+      const expectedEndValues = [1, 5]
       wrapper.findAll('.waveform-chart__track').forEach((track, index) => {
         const endTicks = track.findAll('.waveform-chart__axis--y .tick').filter((tick) => {
           const match = tick.attributes('transform')?.match(/translate\(0,\s*([\d.]+)\)/)

src/components/waveformChartCases/layoutAndDomains.test.ts

@@ -6,6 +6,26 @@ import { resizeObservers } from '../../test/setup'
 import { gridSeries, mountSizedChart } from '../../test/waveformChart'
 
 describe('WaveformChart', () => {
+  it('applies the configured Y-axis split number', async () => {
+    const wrapper = await mountSizedChart(
+      {
+        kind: 'points',
+        points: [
+          { x: 0, y: 3 },
+          { x: 1, y: 97 },
+        ],
+      },
+      { axes: { y: { splitNumber: 5 } } },
+    )
+
+    expect(
+      wrapper
+        .get('.waveform-chart__axis--y')
+        .findAll('.tick text')
+        .map((tick) => tick.text()),
+    ).toEqual(['0', '25', '50', '75', '100'])
+  })
+
   it('expands the Y-axis label gutter for signed values and long exponents', async () => {
     const wrapper = await mountSizedChart(
       {
@@ -296,7 +316,7 @@ describe('WaveformChart', () => {
     expect(wrapper.get('.waveform-chart__axis-endpoint--end').text()).toBe('1000')
   })
 
-  it('reacts to exact fixed Y-domain props and returns to automatic bounds', async () => {
+  it('reacts to nice fixed Y-domain props and returns to automatic bounds', async () => {
     const wrapper = await mountSizedChart({
       kind: 'points',
       points: [
@@ -312,8 +332,8 @@ describe('WaveformChart', () => {
 
     await wrapper.setProps({ yDomain: [3, 97] })
     await flushPromises()
-    expect(yTickLabels()).toContain('3')
-    expect(yTickLabels()).toContain('97')
+    expect(yTickLabels()).toContain('0')
+    expect(yTickLabels()).toContain('100')
 
     await wrapper.setProps({ yDomain: undefined })
     await flushPromises()

src/components/waveformChartCases/legendVisibility.test.ts

@@ -16,13 +16,30 @@ function annotationEditorExists() {
 }
 
 describe('WaveformChart', () => {
+  it('shows legends when a track contains at least two series', async () => {
+    const oneSeries = visibilitySeries()
+    if (oneSeries.kind === 'series') oneSeries.series = oneSeries.series.slice(0, 1)
+    const withoutLegend = await mountSizedChart(oneSeries, {
+      grid: { rowCount: 1, columnCount: 1 },
+    })
+    expect(withoutLegend.findAll('.waveform-chart__legend')).toHaveLength(0)
+
+    const twoSeries = visibilitySeries()
+    if (twoSeries.kind === 'series') twoSeries.series = twoSeries.series.slice(0, 2)
+    const withLegend = await mountSizedChart(twoSeries, {
+      grid: { rowCount: 1, columnCount: 1 },
+    })
+    expect(withLegend.findAll('.waveform-chart__legend')).toHaveLength(1)
+    expect(withLegend.find('.waveform-chart__legend').attributes('data-position')).toBe('top-right')
+  })
+
   it('resolves legend positions by stable track id across pages', async () => {
     const wrapper = await mountSizedChart(
       {
         kind: 'series',
-        series: Array.from({ length: 8 }, (_, index) => ({
+        series: Array.from({ length: 12 }, (_, index) => ({
           id: `series-${index}`,
-          trackId: `frame-${Math.floor(index / 2)}`,
+          trackId: `frame-${Math.floor(index / 3)}`,
           name: `series ${index}`,
           data: {
             kind: 'points' as const,
@@ -75,9 +92,9 @@ describe('WaveformChart', () => {
     const wrapper = await mountSizedChart(
       {
         kind: 'series',
-        series: Array.from({ length: 4 }, (_, index) => ({
+        series: Array.from({ length: 6 }, (_, index) => ({
           id: `series-${index}`,
-          trackId: `frame-${Math.floor(index / 2)}`,
+          trackId: `frame-${Math.floor(index / 3)}`,
           name: `series ${index}`,
           data: {
             kind: 'points',
@@ -112,7 +129,7 @@ describe('WaveformChart', () => {
     })
 
     const items = wrapper.findAll('.waveform-chart__legend-item')
-    expect(items).toHaveLength(2)
+    expect(items).toHaveLength(3)
     expect(items.every((item) => item.attributes('disabled') !== undefined)).toBe(true)
     expect(wrapper.get('.waveform-legend__panel').classes()).not.toContain(
       'waveform-legend__panel--interactive',
@@ -128,7 +145,7 @@ describe('WaveformChart', () => {
       overlayMode: 'multi-axis',
     })
 
-    expect(wrapper.findAll('.waveform-chart__axis--y')).toHaveLength(2)
+    expect(wrapper.findAll('.waveform-chart__axis--y')).toHaveLength(3)
     expect(wrapper.find('[data-annotation-id="high-note"]').exists()).toBe(true)
     const annotationLayer = wrapper.get('.waveform-annotation-layer').element
     const legendLayer = wrapper.get('.waveform-chart__legend-layer').element
@@ -143,8 +160,8 @@ describe('WaveformChart', () => {
 
     expect(
       wrapper.findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['low'])
-    expect(wrapper.findAll('.waveform-chart__axis--y')).toHaveLength(1)
+    ).toEqual(['low', 'mid'])
+    expect(wrapper.findAll('.waveform-chart__axis--y')).toHaveLength(2)
     expect(wrapper.find('[data-annotation-id="high-note"]').exists()).toBe(false)
     expect(wrapper.findAll('.waveform-chart__legend-item')[1].classes()).toContain('is-hidden')
     expect(wrapper.findAll('.waveform-chart__legend-item')[1].attributes('aria-pressed')).toBe(
@@ -170,12 +187,12 @@ describe('WaveformChart', () => {
     )
     flushAnimationFrames()
     await flushPromises()
-    expect(wrapper.findAll('.waveform-chart__tooltip-series')).toHaveLength(1)
+    expect(wrapper.findAll('.waveform-chart__tooltip-series')).toHaveLength(2)
     expect(wrapper.get('.waveform-chart__tooltip-series').text()).toContain('低量程')
 
     await wrapper.findAll('.waveform-chart__legend-item')[1].trigger('click')
     await flushPromises()
-    expect(wrapper.findAll('.waveform-chart__line')).toHaveLength(2)
+    expect(wrapper.findAll('.waveform-chart__line')).toHaveLength(3)
     expect(wrapper.find('[data-annotation-id="high-note"]').exists()).toBe(true)
     expect(wrapper.emitted('series-visibility-change')?.at(-1)).toEqual([
       { seriesId: 'high', visible: true, hiddenSeriesIds: [] },
@@ -191,20 +208,20 @@ describe('WaveformChart', () => {
 
     expect(
       wrapper.findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['low'])
+    ).toEqual(['low', 'mid'])
     await wrapper.findAll('.waveform-chart__legend-item')[0].trigger('click')
     expect(wrapper.emitted('update:hidden-series-ids')?.at(-1)).toEqual([
       ['high', 'temporarily-absent', 'low'],
     ])
     expect(
       wrapper.findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['low'])
+    ).toEqual(['low', 'mid'])
 
     await wrapper.setProps({ hiddenSeriesIds: ['low'] })
     await flushPromises()
     expect(
       wrapper.findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['high'])
+    ).toEqual(['high', 'mid'])
   })
 
   it('retains uncontrolled visibility by stable ID and clears removed IDs', async () => {
@@ -223,7 +240,7 @@ describe('WaveformChart', () => {
     await flushPromises()
     expect(
       wrapper.findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['low'])
+    ).toEqual(['mid', 'low'])
 
     await wrapper.setProps({
       data: {
@@ -234,12 +251,12 @@ describe('WaveformChart', () => {
     await flushPromises()
     await wrapper.setProps({ data: original })
     await flushPromises()
-    expect(wrapper.findAll('.waveform-chart__line')).toHaveLength(2)
+    expect(wrapper.findAll('.waveform-chart__line')).toHaveLength(3)
   })
 
   it('keeps a recoverable legend and stops chart interaction when every series is hidden', async () => {
     const wrapper = await mountSizedChart(visibilitySeries(), {
-      defaultHiddenSeriesIds: ['low', 'high'],
+      defaultHiddenSeriesIds: ['low', 'high', 'mid'],
       grid: { rowCount: 1, columnCount: 1 },
       legend: { interactive: true },
       overlayMode: 'multi-axis',
@@ -248,7 +265,7 @@ describe('WaveformChart', () => {
     expect(wrapper.findAll('.waveform-chart__line')).toHaveLength(0)
     expect(wrapper.findAll('.waveform-chart__axis')).toHaveLength(0)
     expect(wrapper.findAll('.waveform-chart__overlay')).toHaveLength(0)
-    expect(wrapper.findAll('.waveform-chart__legend-item')).toHaveLength(2)
+    expect(wrapper.findAll('.waveform-chart__legend-item')).toHaveLength(3)
     expect(wrapper.get('.waveform-track__no-visible-series').text()).toBe('暂无可见曲线')
 
     await wrapper.findAll('.waveform-chart__legend-item')[0].trigger('click')

src/components/waveformChartCases/multiAxisAndPagination.test.ts

@@ -15,6 +15,7 @@ describe('WaveformChart', () => {
           {
             trackId: 'shared-frame',
             name: '普通量程',
+            unit: 'V',
             data: {
               kind: 'points',
               points: [
@@ -26,6 +27,7 @@ describe('WaveformChart', () => {
           {
             trackId: 'shared-frame',
             name: '大量程',
+            unit: 'A',
             data: {
               kind: 'points',
               points: [
@@ -37,6 +39,7 @@ describe('WaveformChart', () => {
           {
             trackId: 'shared-frame',
             name: '小量程',
+            unit: 'T',
             data: {
               kind: 'points',
               points: [
@@ -57,7 +60,11 @@ describe('WaveformChart', () => {
           .map((label) => label.text())
           .filter((label) => label.startsWith('E')),
       ),
-    ).toEqual([[], [expect.stringMatching(/^E\+03 /)], [expect.stringMatching(/^E-04 /)]])
+    ).toEqual([
+      [],
+      [expect.stringMatching(/^E\+03 \(A\) /)],
+      [expect.stringMatching(/^E-04 \(T\) /)],
+    ])
   })
 
   it('reprojects annotations with the Y axis assigned to their series', async () => {
@@ -177,6 +184,18 @@ describe('WaveformChart', () => {
               ],
             },
           },
+          {
+            id: 'reference',
+            trackId: 'frame-1',
+            name: 'REF_CH_1',
+            data: {
+              kind: 'points',
+              points: [
+                { x: 0, y: 0.25 },
+                { x: 1, y: 1.25 },
+              ],
+            },
+          },
         ],
       },
       { frameNumber: 1, grid: { rowCount: 2, columnCount: 1 } },
@@ -186,7 +205,7 @@ describe('WaveformChart', () => {
     expect(tracks).toHaveLength(2)
     expect(
       tracks[0].findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
-    ).toEqual(['primary', 'comparison'])
+    ).toEqual(['primary', 'comparison', 'reference'])
     expect(
       tracks[1].findAll('.waveform-chart__line').map((line) => line.attributes('data-series-id')),
     ).toEqual(['second-frame'])
@@ -203,12 +222,13 @@ describe('WaveformChart', () => {
     expect(legend.findAll('.waveform-chart__legend-item').map((item) => item.text())).toEqual([
       'BT2_2M',
       'TEST_CH_1',
+      'REF_CH_1',
     ])
     expect(
       legend
         .findAll('.waveform-legend__swatch')
         .map((swatch) => swatch.get('path').attributes('stroke')),
-    ).toEqual(['#0960bd', '#2ca02c'])
+    ).toEqual(['#0960bd', '#2ca02c', '#d62728'])
     expect(wrapper.findAll('.waveform-chart__watermark').map((item) => item.text())).toEqual([
       '1',
       '2',
@@ -232,10 +252,11 @@ describe('WaveformChart', () => {
     await flushPromises()
 
     const tooltipSeries = wrapper.findAll('.waveform-chart__tooltip-series')
-    expect(tooltipSeries).toHaveLength(2)
+    expect(tooltipSeries).toHaveLength(3)
     expect(tooltipSeries.map((item) => item.text())).toEqual([
       expect.stringContaining('BT2_2M'),
       expect.stringContaining('TEST_CH_1'),
+      expect.stringContaining('REF_CH_1'),
     ])
   })
 
@@ -268,6 +289,18 @@ describe('WaveformChart', () => {
               ],
             },
           },
+          {
+            id: 'third',
+            trackId: 'shared',
+            name: 'third',
+            data: {
+              kind: 'points',
+              points: [
+                { x: 0, y: 2 },
+                { x: 1, y: 3 },
+              ],
+            },
+          },
         ],
       },
       { grid: { rowCount: 1, columnCount: 1 } },

src/components/waveformChartCases/presentationMode.test.ts

@@ -42,6 +42,19 @@ const presentationData: WaveformData = {
         ],
       },
     },
+    {
+      id: 'mid',
+      trackId: 'shared',
+      name: '中量程',
+      data: {
+        kind: 'points',
+        points: [
+          { x: 0, y: 50 },
+          { x: 1, y: 100 },
+          { x: 2, y: 75 },
+        ],
+      },
+    },
     {
       id: 'other',
       name: '其他通道',
@@ -150,9 +163,9 @@ describe('WaveformChart presentation mode', () => {
           cancelable: true,
         }),
       )
-      wrapper.get('.waveform-chart__svg').element.dispatchEvent(
-        new MouseEvent('dblclick', { bubbles: true, cancelable: true }),
-      )
+      wrapper
+        .get('.waveform-chart__svg')
+        .element.dispatchEvent(new MouseEvent('dblclick', { bubbles: true, cancelable: true }))
       await wrapper.get('[data-annotation-id="note"]').trigger('contextmenu', {
         clientX: width / 2,
         clientY: height / 2,

src/components/waveformChartCases/viewportReset.test.ts

@@ -119,6 +119,108 @@ describe('WaveformChart viewport reset', () => {
     expect(wrapper.findAll('.waveform-chart__axis-endpoint--end')[0].text()).toBe('1000')
   })
 
+  it('keeps a controlled shared viewport when the data reference changes', async () => {
+    const wrapper = await mountSizedChart(
+      {
+        kind: 'points',
+        points: [
+          { x: 0, y: 0 },
+          { x: 1, y: 1 },
+        ],
+      },
+      { displayMode: 'separated' },
+    )
+    const chart = wrapper.vm as unknown as {
+      setViewportDomain: (domain: [number, number], trackIndex?: number) => void
+    }
+    chart.setViewportDomain([0.25, 0.75])
+    await flushPromises()
+
+    const startBefore = Number(wrapper.get('.waveform-chart__axis-endpoint--start').text())
+    const endBefore = Number(wrapper.get('.waveform-chart__axis-endpoint--end').text())
+    expect(startBefore).toBeGreaterThan(0)
+    expect(endBefore).toBeLessThan(1000)
+
+    await wrapper.setProps({
+      data: {
+        kind: 'points',
+        points: [
+          { x: 0, y: 10 },
+          { x: 1, y: 11 },
+        ],
+      },
+    })
+    await flushPromises()
+
+    expect(Number(wrapper.get('.waveform-chart__axis-endpoint--start').text())).toBeCloseTo(
+      startBefore,
+      10,
+    )
+    expect(Number(wrapper.get('.waveform-chart__axis-endpoint--end').text())).toBeCloseTo(
+      endBefore,
+      10,
+    )
+  })
+
+  it('keeps independently controlled track viewports when the data reference changes', async () => {
+    const wrapper = await mountSizedChart(gridSeries(2), {
+      displayMode: 'independent',
+      grid: { rowCount: 1, columnCount: 2 },
+    })
+    const chart = wrapper.vm as unknown as {
+      setViewportDomain: (domain: [number, number], trackIndex?: number) => void
+    }
+    chart.setViewportDomain([0.2, 0.8], 0)
+    chart.setViewportDomain([0.1, 0.9], 1)
+    await flushPromises()
+
+    const endpoints = () =>
+      wrapper.findAll('.waveform-chart__track').map((track) => ({
+        start: track.get('.waveform-chart__axis-endpoint--start').text(),
+        end: track.get('.waveform-chart__axis-endpoint--end').text(),
+      }))
+    const endpointsBefore = endpoints()
+    expect(Number(endpointsBefore[0].start)).toBeGreaterThan(0)
+    expect(Number(endpointsBefore[0].end)).toBeLessThan(1000)
+    expect(Number(endpointsBefore[1].start)).toBeGreaterThan(0)
+    expect(Number(endpointsBefore[1].end)).toBeLessThan(1000)
+
+    await wrapper.setProps({ data: gridSeries(2) })
+    await flushPromises()
+
+    const endpointsAfter = endpoints()
+    endpointsAfter.forEach((endpoint, index) => {
+      expect(Number(endpoint.start)).toBeCloseTo(Number(endpointsBefore[index].start), 10)
+      expect(Number(endpoint.end)).toBeCloseTo(Number(endpointsBefore[index].end), 10)
+    })
+  })
+
+  it('ignores invalid domains and applies viewport constraints', async () => {
+    const wrapper = await mountSizedChart(
+      {
+        kind: 'points',
+        points: [
+          { x: 0, y: 0 },
+          { x: 1, y: 1 },
+        ],
+      },
+      { displayMode: 'separated', minZoomSpan: 0.2 },
+    )
+    const chart = wrapper.vm as unknown as {
+      setViewportDomain: (domain: [number, number], trackIndex?: number) => void
+    }
+    chart.setViewportDomain([Number.NaN, 0.5])
+    await flushPromises()
+    expect(wrapper.get('.waveform-chart__axis-endpoint--start').text()).toBe('0')
+    expect(wrapper.get('.waveform-chart__axis-endpoint--end').text()).toBe('1000')
+
+    chart.setViewportDomain([0.49, 0.51])
+    await flushPromises()
+    const start = Number(wrapper.get('.waveform-chart__axis-endpoint--start').text())
+    const end = Number(wrapper.get('.waveform-chart__axis-endpoint--end').text())
+    expect(end - start).toBeGreaterThanOrEqual(200)
+  })
+
   it('resets shared and independent explicit domains to their included nice bounds', async () => {
     const shared = await mountSizedChart(
       {

src/data/simulatedWaveforms.test.ts

@@ -3,7 +3,7 @@ import { describe, expect, it } from 'vitest'
 import { createSimulatedWaveformData } from './simulatedWaveforms'
 
 describe('simulated waveform data', () => {
-  it('creates deterministic, finite six-channel data', () => {
+  it('creates deterministic, finite seven-channel data with a two-series second frame', () => {
     const first = createSimulatedWaveformData()
     const second = createSimulatedWaveformData()
 
@@ -11,8 +11,12 @@ describe('simulated waveform data', () => {
     expect(first.kind).toBe('series')
     if (first.kind !== 'series') return
 
-    expect(first.series).toHaveLength(6)
-    expect(new Set(first.series.map((series) => series.id)).size).toBe(6)
+    expect(first.series).toHaveLength(7)
+    expect(new Set(first.series.map((series) => series.id)).size).toBe(7)
+    const secondFrame = first.series.filter(
+      (series) => series.trackId === 'simulated-harmonic-frame',
+    )
+    expect(secondFrame).toHaveLength(2)
     expect(new Set(first.series.map((series) => series.shotNo))).toEqual(new Set(['13300']))
     first.series.forEach((series) => {
       expect(series.data.kind).toBe('points')

src/data/simulatedWaveforms.ts

@@ -13,7 +13,7 @@ type ErrorGenerator = (
 
 interface SimulatedSeriesDefinition extends Pick<
   WaveformSeries,
-  'id' | 'shotNo' | 'name' | 'unit' | 'lineType' | 'pointType' | 'errorBar'
+  'id' | 'trackId' | 'shotNo' | 'name' | 'unit' | 'color' | 'lineType' | 'pointType' | 'errorBar'
 > {
   signal: SignalGenerator
   errors?: ErrorGenerator
@@ -60,6 +60,7 @@ const seriesDefinitions: SimulatedSeriesDefinition[] = [
   },
   {
     id: 'simulated-harmonic',
+    trackId: 'simulated-harmonic-frame',
     shotNo: '13300',
     name: '谐波扰动',
     unit: 'V',
@@ -68,6 +69,18 @@ const seriesDefinitions: SimulatedSeriesDefinition[] = [
     signal: (time) =>
       0.9 * Math.sin(TWO_PI * 0.55 * time) + 0.28 * Math.sin(TWO_PI * 2.2 * time + 0.4),
   },
+  {
+    id: 'simulated-harmonic-reference',
+    trackId: 'simulated-harmonic-frame',
+    shotNo: '13300',
+    name: '谐波对比',
+    unit: 'V',
+    color: '#2ca02c',
+    lineType: 'linear',
+    pointType: 'none',
+    signal: (time) =>
+      0.62 * Math.sin(TWO_PI * 0.55 * time + 0.55) + 0.18 * Math.sin(TWO_PI * 2.2 * time - 0.2),
+  },
   {
     id: 'simulated-damped',
     shotNo: '13300',

src/test/waveformChart.ts

@@ -58,6 +58,18 @@ export function visibilitySeries(): WaveformData {
           ],
         },
       },
+      {
+        id: 'mid',
+        trackId: 'shared-frame',
+        name: '中量程',
+        data: {
+          kind: 'points',
+          points: [
+            { x: 0, y: 100 },
+            { x: 1, y: 200 },
+          ],
+        },
+      },
     ],
   }
 }

src/types/chart.ts

@@ -174,6 +174,8 @@ export interface WaveformAxesOptions {
   }
   y?: {
     lineVisible?: boolean
+    /** Target total number of equal Y-axis ticks, including endpoints. Defaults to 5. */
+    splitNumber?: number
   }
 }
 

src/utils/formatters.test.ts

@@ -40,6 +40,15 @@ describe('waveform number formatters', () => {
     expect(formatScientificAxisExponent(0.0001, 0.0003)).toBe('E-04')
   })
 
+  it('appends a unit to the top tick with or without scientific notation', () => {
+    expect(formatScientificAxisLabel(3000, { axisMin: 1000, axisMax: 3000, unit: 'V' })).toBe(
+      'E+03 (V) 3',
+    )
+    expect(formatScientificAxisLabel(3, { axisMin: 0, axisMax: 3, unit: 'A' })).toBe('(A) 3')
+    expect(formatScientificAxisLabel(2, { axisMin: 0, axisMax: 3, unit: 'A' })).toBe('2')
+    expect(formatScientificAxisLabel(3, { axisMin: 0, axisMax: 3, unit: '  ' })).toBe('3')
+  })
+
   it('derives the exponent from the largest absolute endpoint', () => {
     expect(resolveScientificAxisExponent(-9000, -1000)).toBe(3)
     expect(resolveScientificAxisExponent(-100_000, -3000)).toBe(5)

src/utils/formatters.ts

@@ -11,6 +11,7 @@ export interface ScientificAxisLabelOptions {
   axisMin?: number
   axisMax?: number
   topTickValue?: number
+  unit?: string
 }
 
 /** @deprecated Use ScientificAxisLabelOptions. */
@@ -71,9 +72,11 @@ export function formatScientificAxisLabel(
   const scaledValue = exponent === null ? value : value / 10 ** exponent
   const formattedValue = formatYAxisNumber(scaledValue)
   const topTickValue = options.topTickValue ?? options.axisMax
-  return exponent !== null && value === topTickValue
-    ? `${formatExponent(exponent)} ${formattedValue}`
-    : formattedValue
+  if (value !== topTickValue) return formattedValue
+  const unit = options.unit?.trim()
+  const unitLabel = unit ? `(${unit}) ` : ''
+  const exponentLabel = exponent === null ? '' : `${formatExponent(exponent)} `
+  return `${exponentLabel}${unitLabel}${formattedValue}`
 }
 
 /** Return the shared E-style multiplier for an axis, or null for a plain axis. */