"Scott S" <[EMAIL PROTECTED]> wrote in message 
news:<B7XS9.241514$[EMAIL PROTECTED]>...
> Does anyone know the formula for recursively calculating standard deviation?

I use

Nnew = Nold + 1
Mnew = Mold + (xnew-Mold)/Nnew
Vnew = Vold + [(xnew-Mold)(xnew-Mnew)-Vold]/Mold
Snew = sqrt(Vnew)

Hope this helps.

Greg
.
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