# Documentation/How Tos/Calc: POISSON function

From Apache OpenOffice Wiki

## POISSON

Calculates values for a Poisson distribution.

### Syntax:

**POISSON(x; λ; mode)**

- The Poisson distribution is a discrete probability distribution giving the probability that
events occur in a certain time, where events occur independently, and where on average**x**events are expected.**λ**should be >=0 and**x**should be >0.**λ**should be integer.**x**

### Example:

**POISSON(8; 9; 0)**

- returns approximately 0.1317, the probability that exactly 8 events occur in a time period where you expect 9 events.

**POISSON(8; 9; 1)**

- returns approximately 0.4556, the probability that up to and including 8 events occur in a time period where you expect 9 events.