A Poisson experiment is something that examines the number of times an event occurs during a specified interval. The interval could be literally anything – a unit of time, length, volume, etc. We might, for example, ask how many customers visit a restaurant each day, or how many home sixes are hit in a tournament of cricket.

The number of successes in a Poisson experiment is referred to as a Poisson random variable. A Poisson distribution is a probability distribution of a Poisson random variable.

All you need to do is to enter 2 values into the calculator- one in the Poisson random variable (say x= 8) column and the other in the Average rate of success column. Then click on the calculate button and voila!The calculator will automatically compute the Poisson Probability: P(X=8), the Cumulative Probabilities for: P(X < 8), P(X < 8), P(X > 8), P(X > 8). It is that simple.