# Delta (/docs/charts/delta)

Delta is a text-first metric: a signed number with a direction glyph. It reads inline, next to a KPI, or inside a table
cell. Direction is always doubled — a triangle _and_ a color — so it never relies on color alone.

```tsx
<span className="text-lg">
  <Delta value={0.124} title="Revenue vs last week" />
</span>
```

## Install

```tsx
import { Delta } from "@microcharts/react/delta";

<Delta value={0.124} title="Revenue vs last week" />
```

Setup (package + stylesheet): [Quickstart](/docs/quickstart#set-up-with-an-ai-agent) or paste [`/agent-setup.md`](/agent-setup.md) into your agent.


## When to use it

- **Good for** — a KPI's change, period-over-period percent, inline metric movement.
- **Avoid for** — showing a series or comparing magnitudes across items.

## Sizing

Delta is text, not a fixed box — it takes the `font-size` of whatever wraps it and its glyph scales in `em`. Size it by
the surrounding type: inline, it inherits the sentence; beside a KPI figure, lift the font-size to match.

## Variants

`from` derives a percent change; `positive="down"` flips only the color for metrics where down is good (latency, churn,
cost).

```tsx
<Delta value={0.124} />
```

```tsx
<Delta value={128} from={100} />
```

```tsx
<Delta value={-0.08} />
```

```tsx
<Delta value={-0.05} positive="down" />
```

`format` also takes `Intl.NumberFormatOptions` — with a `locale`, the magnitude follows that locale's own grouping and
decimal marks (a German reader sees a comma decimal and a space before the `%`, not a period). The leading sign is the
library's own `+` / `−`, so it reads the same in every locale.

```tsx
<Delta value={0.124} format={{ style: "percent", maximumFractionDigits: 1 }} locale="de-DE" />
```

## Edge cases

```tsx
<Delta value={0} />
```

```tsx
<Delta value={Number.NaN} />
<Delta value={Infinity} />
```

A zero delta shows the flat glyph and **"No change."** — never a `+0%`/`−0%` that implies a direction with nothing
behind it. `NaN` and `±Infinity` degrade the same way: the flat glyph, an em dash instead of a number, and **"No
change."** rather than a misleading `NaN%`.


## Why this default

Direction is always double-encoded — the triangle's shape carries it as much as the color does — because a
red/green-only read fails for color-blind viewers and under `forced-colors`. `positive` flips only which color means
"good"; it never changes which way the glyph points, so a metric where down is good (latency, churn, cost) still shows
an honest down-pointing triangle, just in the "good" color. Percent is the default format because most deltas are
relative change, not raw magnitude — pass `format` for currency, counts, or any other unit. Non-finite input renders as
an em dash rather than `NaN%`, because a broken number should read as "nothing to report," not as a fabricated value.

## Accessibility

Delta renders accessible inline text — the glyph is decorative and the value carries the meaning. Color is a redundant
channel on top of the direction glyph and the sign, so the change survives forced-colors and color-blind viewing. The
interactive entry re-announces the figure through a polite live region when the value changes.

This chart is a single unit, so there is nothing to rove between: a click, tap, `Enter` or `Space` selects it
and fires `onSelect`, and no selection stays pinned. That is the scalar half of the shared
[interaction contract](/docs/accessibility#one-interaction-contract).

## Props

| Prop | Type | Description |
| --- | --- | --- |
| `value` (required) | `number` | The change, or current value when from is set. |
| `from` | `number` | Prior value; Delta shows the percent change. |
| `positive` | `"up" \| "down"` | Which direction is good (colors only). |
| `format` | `Intl.NumberFormatOptions \| fn` | Number formatting. |
| `locale` | `string \| string[]` | BCP 47 locale(s) for the formatted number. |
| `summary` | `string \| false` | Override or disable the auto summary. |
| `animate` | `boolean` | (interactive) Opt-in entrance motion when the chart mounts client-side — add `import "@microcharts/react/motion"` once. Inert on the server, on hydrated server HTML, and under `prefers-reduced-motion`. |

Plus the shared grammar — `data`, `domain`, `color`, `title`, `summary`, `format` — and the layout props (`width`, `height`, `className`, `style`) that every chart accepts. Interactive entries also share `animate` and `live`, and — wherever a chart has more than one navigable unit — `onActive`, `onSelect`, `selectedIndex` and `defaultSelectedIndex`; and — wherever the chart shows a hover value — `readout`. See [the shared grammar](/docs/quickstart#the-shared-grammar).