The STDEV statistic in HM2 is unusual. I can explain that where STDEV = 20BB in HM1 it becomes 2.0BB in Hm2. I actually contacted them directly and was not satisfied by their responses.

Here's a basic explanation of how i think about Standard Deviation.

I would tend to continue thinking of it as being 20BB because its more useful and practical.

In this respect, lets say you play 100 hands of poker and measure your winrate per 100 hands (ie your result after that sample).

Well, with a SD = 20BB, we can expect your results to deviate around your true winrate between +/-20BB 68% of the time.

In other words, if our winrate is 1BB/100 then roughly 2/3rds of the time, our results over 100 hands will lie between -19BB and 20BB.

95% of the time, we can expect your results over 100 hands to fall between +/- 40BB around your true winrate.

In other words, standard deviation (STDEV) is a measure of the extent of the dispersion in a distribution. The distribution in this case, is the complete set of results expressed in BB/100 for possible 100 hands samples of poker played by you.

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