POISSON

POISSON(x, mean, cumulative)

Returns the probability distribution function OR the cumulative probability function for a poisson distribution.

x	The number of events.
mean	The expected numeric value.
cumulative	A logical value indicating the type of function to use: False (or 0) = individual probability (equal to) True (<> 0) = cumulative probability (equal to or less than)

REMARKS

* This function is only available for backwards compatibility and should not be used.
* POISSON.DIST was added in Excel 2010 to replace this function.
* The poisson distribution is a discrete distribution
* If "x" is not an integer, it is truncated.
* If "x" is not numeric, then #VALUE! is returned.
* If "mean" is not numeric, then #VALUE! is returned.
* If "mean" = 0, then #NUM! is returned.
* If "x" < 0, then #NUM! is returned.
* If "x" = 0, then
* If "cumulative" = False, then the height of the curve at "x" is returned.
* If "cumulative" = True, then the area under the curve to the left of "x" is returned.
* For the Microsoft documentation refer to support.microsoft.com

	A
1	=POISSON(2, 5, FALSE) = 0.084
2	=POISSON(2, 5, TRUE) = 0.125
3	=POISSON(2, 2, 1) = 0.677
4	=POISSON(-2, 2, 1) = #NUM!