# stepRate

> Pumping rate of step index (default the first), or null.

> **stepRate**(`event`, `index?`): `number` \| `null`

Pumping rate of step `index` (default the first), or `null`.

## Parameters

### event

`HydrodynamicEvent`

### index?

`number` = `0`

## Returns

`number` \| `null`