# subtract

Subtract a Duration from the current state of a RefDuration.

## Signatures

```ts
export declare const subtract: {
    (that: Duration.Duration): <E, R>(ref: RefDuration<E, R>) => RefSubject.Computed<Duration.Duration, E, R>;
    <E, R>(ref: RefDuration<E, R>, that: Duration.Duration): RefSubject.Computed<Duration.Duration, E, R>;
};
```

## Why

Subtract a Duration from the current state of a RefDuration. The operation remains attached to
the RefSubject's versioned state boundary.

## Ownership and lifetime

The subtract view retains no independent state. An Effect read samples the source once; Fx
observation follows later pushes and its observing Scope owns subscription cleanup.