# POISSON

Calculates values for a Poisson distribution.

### Syntax:

POISSON(x, λ, mode)

The Poisson distribution is a discrete probability distribution giving the probability that x events occur in a certain time, where events occur independently, and where on average λ events are expected. x should be >=0 and λ should be >0. x should be integer.
If mode is 0, POISSON calculates the probability density function of the Poisson distribution:

If mode is 1, POISSON calculates the cumulative distribution function of the Poisson distribution:

### 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.