Poisson Command

Poisson( <Mean> ): Returns a bar graph of a Poisson distribution with given mean λ.
Poisson( <Mean>, <Boolean Cumulative> ): Returns a bar graph of a Poisson distribution when Cumulative = false. Returns a graph of a cumulative Poisson distribution when Cumulative = true. The first parameter is same as above.
Poisson( <Mean>, <Variable Value v>, <Boolean Cumulative> ): Let X be a Poisson random variable. Returns P( X = v) when Cumulative = false. Returns P( X ≤ v) when Cumulative = true. First parameter is same as above.

Poisson(3, 1, true) yields 0.2 in the Algebra View and $\frac{4}{e³}$ in the CAS View.
Poisson(3, 1, false) yields 0.15 in the Algebra View and $\frac{3}{e³}$ in the CAS View.

A simplified syntax is available to calculate P(u ≤ X ≤ v): e.g. Poisson(1, 1..5) yields 0.63153, that is the same as Poisson(1, {1, 2, 3, 4, 5}).