I thought *SURE* I knew an algorithm once, long ago, for calculating the SD "on the fly", but I can't remember any details of any such trickery and a quick Google search only came up with algorithms that I already know and that start with the obvious "calculate the mean..." Basically, I have a largish data set that it will only be convenient to read once and I'd like to be able to calculate [or at least estimate] the SD as the data comes by and avoid having to scroll it into a temp file and then do a second pass over the data from the temp file... Is there such an algorithm or am I just misremembering? Thanks! /Bernie\ -- Bernie Cosell Fantasy Farm Fibers mailto:bernie@fantasyfarm.com Pearisburg, VA --> Too many people, too few sheep <--