Duration axis

Some charts aren't about when — they're about how far in. A workout, a lab run, a load test, a race: nobody reads "the heart rate at 10:38", they read "the heart rate five minutes in". <ChartContainer origin> relabels the shared x axis as offsets from a zero point, so the strip reads

00:00   00:05   00:10

where it used to read

10:35   10:40   10:45

src/examples/charts-duration-axis.tsx
import {
  ChartContainer,
  ChartRow,
  Layers,
  LineChart,
  XAxis,
  YAxis,
} from '@pond-ts/charts';
import { TimeSeries } from 'pond-ts';
import { useSiteChartTheme } from '@site/src/theme/useSiteChartTheme';

/** A ride that started at 10:33:17 — a deliberately un-round instant, so the
 *  duration labels and the wall-clock labels can't be confused. */
const START = Date.UTC(2026, 0, 15, 10, 33, 17);

function ride() {
  const rows: Array<[number, number]> = [];
  for (let i = 0; i < 73; i += 1) {
    rows.push([START + i * 10_000, 138 + 22 * Math.sin(i / 8) + (i % 3)]);
  }
  return new TimeSeries({
    name: 'ride',
    schema: [
      { name: 'time', kind: 'time' },
      { name: 'hr', kind: 'number' },
    ] as const,
    rows,
  });
}

export default function ChartsDurationAxis() {
  const theme = useSiteChartTheme();

  return (
    <ChartContainer showAxis={false} width={560} theme={theme} origin="data">
      <ChartRow height={200}>
        <YAxis id="hr" label="bpm" width={44} />
        <Layers>
          <LineChart series={ride()} column="hr" axis="hr" />
        </Layers>
      </ChartRow>
      {/* The primary strip reads durations from the ride's first sample. */}
      <XAxis label="Elapsed" />
      {/* A second strip on the SAME origin-anchored ticks: a d3 time specifier
          can only describe an instant, so it labels the wall clock underneath. */}
      <XAxis format="%H:%M" />
    </ChartContainer>
  );
}

That example stacks both strips on purpose — durations on top, the wall clock underneath, one shared tick set. See Two label systems, one scale below.

`origin`

Value	Zero point	Use it for
`'data'`	The start of the data (the union of the layers' x extents)	"Since the beginning of the series" — the common case. Stays put as you pan.
a `number`	An explicit instant / axis value	A gun, a trigger, a lap marker. Ticks before it read negative (`-00:05`).

<ChartContainer width={620} origin="data">
  <ChartRow height={180}>
    <YAxis id="hr" label="bpm" />
    <Layers>
      <LineChart series={ride} column="hr" axis="hr" />
    </Layers>
  </ChartRow>
  <XAxis label="Elapsed" />
</ChartContainer>

origin lives on the container, not on <XAxis>, because the container owns the shared x geometry: the ticks it resolves are the ones the axis labels and the ones the gridlines draw at. Put the origin on one axis and you'd get labels at 00:05 over a gridline at 10:35.

Labelling, not transforming

origin changes two things and only two: where the ticks sit and what they say. Everything else stays in absolute axis units — a range, a <Marker at>, an onRegionSelect span, trackerPosition, the data itself. There is no second coordinate system to keep straight; you never convert.

Ticks sit at round durations, measured from the origin

This is the part that a formatter alone can't do. A ride starting at 10:33:17 gets ticks at 10:33:17, 10:38:17, 10:43:17 — so its labels read 00:00, 00:05, 00:10. Placing the ticks on wall-clock boundaries instead and just relabelling them would give 00:01:43, 00:06:43, 00:11:43: technically correct, unreadable.

The step comes off a duration ladder — the intervals a clock actually subdivides by — rather than the 1-2-5 ladder a linear axis uses:

1 / 2 / 5 / 10 / 20 / 50 / 100 / 200 / 500 ms · 1 / 2 / 5 / 10 / 15 / 30 s · 1 / 2 / 5 / 10 / 15 / 30 min · 1 / 2 / 3 / 6 / 12 h · then 1-2-5 whole days

Calendar months are deliberately not a rung: an elapsed axis measures duration, and "one month later" isn't one.

Label shapes

The step picks the finest component shown, the axis's magnitude picks the coarsest. A minute-or-coarser step heads the clock with hours even when they're zero (00:05 — five minutes in), because that's the shape of the wall-clock axis it replaces; only an axis fine enough for seconds drops to MM:SS.

Axis	Reads
2 s, 40 ms steps	`00:00.000` `00:00.500`
90 s, 15 s steps	`00:15` `00:30` `00:45`
2 h, 30 s steps	`01:01:30`
10 min, 5 min steps	`00:00` `00:05` `00:10`
6 h, 1 h steps	`01:00` `02:00`
3 days, 12 h steps	`12:00` `1d 00:00` `1d 12:00`
30 days, 5 day steps	`0d` `5d` `10d`

The day part appears only once there is one — the same promotion-at-the-turn the flat date style makes on a calendar axis.

The cursor reads one grain finer

Ticks stay terse; the crosshair pill and <Marker indicator> pills add seconds — 00:05:12 under a 00:05 axis. Same shape, more precision: the elapsed twin of the grain-aware readout a calendar axis gives you. A container cursorFormat still overrides it, and a cursorFormat function receives the elapsed default as its defaultText.

Two label systems, one scale

An explicit format wins over the duration default — and on a time axis, a d3 time specifier can only describe an instant, so it labels the wall clock underneath. That's the lever, not a limitation: declare two <XAxis> strips and you get durations and wall clock on one shared, origin-anchored tick set.

<XAxis label="Elapsed" />
<XAxis format="%H:%M" color="#8b8fa3" />

For a label the library doesn't offer, pass a function — it receives the raw axis value and owns the whole label:

<ChartContainer origin="data" timeFormat={(t) => `${Math.round((t - start) / 60_000)}m`}>

On a value axis

The same prop, the same walk: ticks anchored at the origin on the 1-2-5 ladder, labels reading the offset. A ride logged from 1,200 m reads distance travelled (0 … 4,000) instead of distance recorded (2,000 … 5,000). Here a number specifier describes the offset perfectly well, so <XAxis format> formats the offset rather than the absolute value.

<ChartContainer width={560} origin="data">
  {/* series is a ValueSeries — see the value-axis page */}
  <XAxis label="Metres ridden" />
</ChartContainer>

Sharp edges

Trading calendars. On a trading-time axis the durations are wall-clock, so ticks spanning a collapsed session gap sit unevenly across the seam. Elapsed trading time (five hours of market time) isn't implemented.
Category axes have no numeric origin to offset from; origin is ignored.
The origin is the data's, not the view's. Pan past the first sample and the labels go negative rather than re-zeroing at the left edge. A view-anchored mode isn't implemented.

origin​

Labelling, not transforming​

Ticks sit at round durations, measured from the origin​

Label shapes​

The cursor reads one grain finer​

Two label systems, one scale​

On a value axis​

Sharp edges​

See also​