Standard deviation

I am looking at stockcharts.com 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:

https://statistics.laerd.com/statistical-guides/measures-of-spread-standard-deviation.php

https://www.khanacademy.org/math/statistics-probability/summarizing-quantitative-data/variance-standard-deviation-sample/a/population-and-sample-standard-deviation-review

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