> Anybody got a good averaging algorithm?
>
> NEWAVG = {(AVG*255)+DATA}/256
>
A better way is to actually keep that sum of the last 256 reading
rather that multiplying the average by 255.  Thus you have

NEWACCUM = (ACCUM - ACCUM/256) + DATA;
AVG = NEWACCUM/256;

Keeping those extra 8 bits around all the time reduces that error
you noticed by your effect truncation of these least significant
8 bits.

Dave Reinagel