AVR-Chat

> Mean of N samples is (1/N) sum(Xi) where Xi is one of the samples X0, X1,
> ... XN-1

Right, I've got that working, but they're telling me that they do NOT
maintain any history other than their mean and standard deviation
values!
I'm also told (last 10 mins) that they are not using the words "mean"
and "standard deviation" in the classical sense.

> Now if you are doing a total mean rather than a windowed mean (most recent
> N samples), then the new mean value is
>
> Mean = (N*MeanPrevious + Xnew)/(N+1)

Right.

> Not sure that there is a way to do this for standard deviation because if
> the mean changes, then all the difference values change. That is the  hard
>  part.

That's what's bugging me.. It looks like I could chew up an AVR
processing a small number of sensors this way, yet they do it with
multiple megapixel images in realtime. (granted, on quad-core
machines... but...)