> ## 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.

# idelta_left()

> Calculate the instantaneous 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 change at the left, or earliest, edge of a counter aggregate. This is equal to the second
value minus the first value, after accounting for resets.

## Samples

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

```sql theme={"dark"}
SELECT
    id,
    bucket,
    idelta_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"}
idelta_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                                                                     |
| ------------ | ---------------- | ------------------------------------------------------------------------------- |
| idelta\_left | DOUBLE PRECISION | The instantaneous delta 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