How the checkraise hud is calculated ?

[vinally]

I would like to know how the checkraise is calculated. very often you always see in pop up, like this below

checkraise = 5% (20 ) . how you get 5% and 20 in bracket?

This is very important for me to know.

[netsrak]

20 is the sample size. For 20 hands with a possible checkraise vill. made it in 5% = 1 hand out of this 20