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Add type annotation and compound unit docs to dim-si README #5

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Add type annotation and compound unit docs to dim-si README #5

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32 changes: 32 additions & 0 deletions packages/dim-si/README.md
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Expand Up @@ -109,6 +109,38 @@ const picogram = gram.scaled(PICO);

See [prefixes.ts](./src/prefixes.ts) for all available SI prefixes.

## Type Annotations

Each unit module exports a dimension type (e.g., `Length`, `Velocity`). Wrap
these with `Quantity` to annotate function parameters and return types:

```typescript
import type { Quantity } from "@isentropic/dim-quantity";
import type { Length } from "@isentropic/dim-si/length";
import type { Time } from "@isentropic/dim-si/time";
import type { Velocity } from "@isentropic/dim-si/velocity";
import { divide } from "@isentropic/dim-si/ops";

function speed(
distance: Quantity<Length>,
duration: Quantity<Time>,
): Quantity<Velocity> {
return divide(distance, duration);
}
```

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@gdtroszak gdtroszak Feb 12, 2026

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This feels like it could live in the Quick Start rather than its own section — it's a natural next step after using built-in units.

## Compound Units

Create units like `km/h` by combining scale factors from existing units:

```typescript
import { kilometer } from "@isentropic/dim-si/length";
import { hour } from "@isentropic/dim-si/time";
import { meterPerSecond } from "@isentropic/dim-si/velocity";

const kilometerPerHour = meterPerSecond.scaled(kilometer.scale / hour.scale);
```

## Adding a New Unit

Units are organized one file per dimension. To add a new unit to an existing
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