Standard deviation

I am looking at standard deviation and have some ideas to play wiht. I notice that there are 2 options for standard deviations in afl.
which is the common one that i can compare with what i was trying with stockcharts?
Here is the chart i was looking at with the standard deviation.

AFL has the formula StDev( ARRAY, periods , Population = True )

should i use Population true or false?

Below links will help you: