> ## 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.

# irate_left()

> Calculate the instantaneous rate of change at the left, or earliest, edge of a counter aggregate

<Icon icon="tag" iconType="duotone" /> Since [1.3.0][toolkit-1.3.0]

Calculate the instantaneous rate of change at the left, or earliest, edge of a counter aggregate. This is equal to the
second value minus the first value, divided by the time lapse between the two points, after accounting for resets. This
calculation is useful for fast-moving counters.

## Samples

Get the instantaneous rate of change at the start of each 15-minute counter aggregate.

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

## Arguments

The syntax is:

```sql theme={"dark"}
irate_left(
  summary CounterSummary
) RETURNS DOUBLE PRECISION
```

| Name      | Type             | Default | Required | Description                                                    |
| --------- | ---------------- | ------- | -------- | -------------------------------------------------------------- |
| `summary` | `CounterSummary` | -       | ✔        | A counter aggregate created using [`counter_agg`][counter-agg] |

## Returns

| Column      | Type             | Description                                                                              |
| ----------- | ---------------- | ---------------------------------------------------------------------------------------- |
| irate\_left | DOUBLE PRECISION | The instantaneous rate of change at the left, or earliest, edge of the counter aggregate |

[counter-agg]: /api-reference/timescaledb-toolkit/counters-and-gauges/counter_agg/counter_agg

[toolkit-1.3.0]: https://github.com/timescale/timescaledb-toolkit/releases/tag/1.3.0