I am trying to understand how the worksheet performs its calculations.

I attach the pdf of the IRBT ISSW from 3/14/2018 IRBT_Tssw.pdf (96kb) downloaded 1 time(s).

IRBT_Tssw.pdf (96kb) downloaded 2 time(s).

Just for the Ave Low PE, for example, all of the not-crossed-out entries are less than 19.7 ergo, the Average of those values cannot be 19.7.

Is there a mathematical discussion somewhere of how these calculations are performed? I looked at the sample chapter of the book Take Stock and it seems to simple minded to likely contain this informaiton.