> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify-poc.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# delta()

> Calculate the change in a gauge from a gauge aggregate

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

Get the change in a gauge over a time period. This is the simple delta, computed by subtracting the last seen value from
the first.

## Samples

Get the change in each gauge over the entire time interval in table `foo`.

```sql theme={"dark"}
SELECT
    id,
    delta(summary)
FROM (
    SELECT
        id,
        gauge_agg(ts, val) AS summary
    FROM foo
    GROUP BY id
) t
```

## Arguments

The syntax is:

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

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

## Returns

| Column | Type             | Description                                        |
| ------ | ---------------- | -------------------------------------------------- |
| delta  | DOUBLE PRECISION | The change in the gauge over the bucketed interval |

[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