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# TimeInterval

A number of seconds.

```
typealias TimeInterval = Double
```

## Discussion

A [`TimeInterval`](/documentation/Foundation/TimeInterval) value is always specified in seconds; it yields sub-millisecond precision over a range of 10,000 years.

On its own, a time interval does not specify a unique point in time, or even a span between specific times. Combining a time interval with one or more known reference points yields a [`Date`](/documentation/Foundation/Date) or [`DateInterval`](/documentation/Foundation/DateInterval) value.

---

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