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# gauge_zero_time()

> Calculate the time when the gauge value is predicted to have been zero

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

Calculate the time when the gauge value is modeled to have been zero. This is the x-intercept of the linear fit between
gauge value and time.

## Samples

Estimate the time when the gauge started

```sql theme={"dark"}
SELECT
    id,
    bucket,
    gauge_zero_time(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"}
gauge_zero_time(
    summary GaugeSummary
) RETURNS TIMESTAMPTZ
```

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

## Returns

| Column            | Type        | Description                                                  |
| ----------------- | ----------- | ------------------------------------------------------------ |
| gauge\_zero\_time | TIMESTAMPTZ | The time when the gauge value is predicted to have been zero |

[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