> ## Documentation Index
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> Use this file to discover all available pages before exploring further.

# time_delta()

> Calculate the difference between the first and last times from a gauge aggregate

<Icon icon="flask" /> Early access <Icon icon="tag" iconType="duotone" /> Since [1.6.0][toolkit-1.6.0]

Get the number of seconds between the first and last measurements in a gauge aggregate

## Samples

Get the time difference between the first and last gauge readings for each 15-minute interval. Note this difference
isn't necessarily equal to `15 minutes * 60 seconds / minute`, because the first and last readings might not fall
exactly on the interval boundaries.

```sql theme={"dark"}
SELECT
    id,
    bucket,
    time_delta(summary)
FROM (
    SELECT
        id,
        time_bucket('15 min'::interval, ts) AS bucket,
        gauge_agg(ts, val) AS summary
    FROM foo
    GROUP BY id, time_bucket('15 min'::interval, ts)
) t
```

## Arguments

The syntax is:

```sql theme={"dark"}
time_delta(
    summary GaugeSummary
) RETURNS DOUBLE PRECISION
```

| Name      | Type           | Default | Required | Description                                              |
| --------- | -------------- | ------- | -------- | -------------------------------------------------------- |
| `summary` | `GaugeSummary` | -       | ✔        | A gauge aggregate created using [`gauge_agg`][gauge-agg] |

## Returns

| Column      | Type             | Description                                                  |
| ----------- | ---------------- | ------------------------------------------------------------ |
| time\_delta | DOUBLE PRECISION | The difference, in seconds, between the first and last times |

[gauge-agg]: /api-reference/timescaledb-toolkit/counters-and-gauges/gauge_agg/gauge_agg

[toolkit-1.6.0]: https://github.com/timescale/timescaledb-toolkit/releases/tag/1.6.0