# PoissonInv Script and chart function

`PoissonInv()` returns the inverse of the accumulated probability of the Poisson distribution.

Syntax:

PoissonInv(prob, mean)

Return data type: number

Arguments

| Argument | Description |
| --- | --- |
| `prob` | A probability associated with the Poisson-probability distribution. It must be a number between 0 and 1. |
| `mean` | A positive number defining the average outcome. |

This function is related to the `PoissonDIST` function in the following way:   
`If prob = PoissonDist(value, mean), then PoissonInv(prob, mean) = value`