As far as I know “mean” and “average” are synonymous. Let me know if that’s not the case, and also drop me a link for how to calculate one vs. the other.
Graphing the variance between two devices is not currently possible, but an interesting concept. There’s no reason why a series on the time series graph couldn’t be a calculation of two other series. Will brainstorm on this internally.
A workaround for now will be to record the variance of two devices onto a third virtual device, which can then be graphed.