see 
https://github.com/jamescprice/131-APL-Games-for-your-Commodore-64-C128-and-SuperPET/blob/main/131%20APL%20Games/025%20DSTAT/dstatresults.png

https://en.wikipedia.org/wiki/Standard_deviation

https://groups.io/g/Channel-F-and-VideoBrain/attachment/21/0/ALPS-Brochure.pdf

https://archive.org/details/More_Than_32_BASIC_Programs_for_the_Commodore_64/page/n296/mode/1up

https://www.mathsisfun.com/data/standard-deviation-formulas.html
