# TrendArrow (/docs/charts/trend-arrow)

TrendArrow answers "which way is this moving?" at glyph size. The shape _is_ the direction — up, down, or a flat bar —
and color only reinforces it, so the read survives grayscale, print, and forced-colors. When the magnitude matters,
reach for [Delta](/docs/charts/delta) instead.

```tsx
import { TrendArrow } from "@microcharts/react/trend-arrow";

<TrendArrow
  value={-0.08}
  positive="down"
  format={{ style: "percent", maximumFractionDigits: 0 }}
  title="Latency vs last week"
/>
```

## Install

```tsx
import { TrendArrow } from "@microcharts/react/trend-arrow";

<TrendArrow value={-0.08} positive="down" title="Latency 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** — table direction columns, dense dashboards, inline movement cues.
- **Avoid for** — exact magnitudes (Delta) or series shape (Sparkline).

## Sizing

The glyph is a fixed 16-unit box that scales like an image — size it with CSS. With `showValue` the viewBox widens to
reserve a gutter for the number, so text never paints outside the chart.

## Variants

Three glyph weights for three densities, an honest noise floor, and the number when the glyph alone is too terse.

```tsx
<TrendArrow value={1} glyph="arrow" />
<TrendArrow value={1} glyph="triangle" />
<TrendArrow value={1} glyph="chevron" />
```

```tsx
// |value| ≤ flatBand reads as "no real change" — a declared noise floor
<TrendArrow value={0.01} flatBand={0.02} />
```

```tsx
<TrendArrow value={0.12} showValue format={{ style: "percent", maximumFractionDigits: 0 }} />
```

```tsx
<TrendArrow value={-0.08} positive="down" />
```

## Edge cases

```tsx
<TrendArrow value={0} showValue />
```

```tsx
<TrendArrow value={Number.NaN} showValue />
```

```tsx
<TrendArrow value={12483} showValue format={{ maximumFractionDigits: 0 }} locale="de-DE" />
```

`format`/`locale` reach `showValue`'s number and the accessible summary's magnitude together — "12,483" becomes "12.483"
in German grouping.


## Why this default

The arrow (shaft + head) stays legible at 8 px and in forced-colors where lighter marks blur; the glyph never scales
with magnitude — an arrow twice as long would be a lie at this precision. `flatBand` exists so tiny wiggles don't read
as movement: declare your noise floor instead of letting every ±0.1% look like a trend.

## Accessibility

The default accessible name is the factual direction — **"Up 12%."**, **"No change."** within the flat band, **"No
data."** for non-finite input. `positive="down"` flips only the color, never the glyph or the words. The interactive
entry announces direction changes through a polite live region and pulses the glyph (gated on reduced motion).

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` | Signed change; sign → direction, magnitude only via showValue/summary. |
| `flatBand` | `number` | Noise floor: \|value\| ≤ flatBand renders the flat glyph. |
| `glyph` | `"arrow" \| "triangle" \| "chevron"` | Mark weight: default legibility, dense cells, inline text. |
| `showValue` | `boolean` | Append the formatted value in a right gutter. |
| `positive` | `"up" \| "down"` | Which direction is good (colors only, never the glyph). |
| `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).