RMS has nothing to do with zero crossings, it has to do with time. Just
measure, square, and add the voltages for a second, then sqrt and divvy by
the number of samples. Neither the start nor the end have anything to do
with zero crossings.

You can make a cuontinuous-reading RMS meter using the stream of read data
back to 1 second - 1 sample time. With each new sample you get another
'second' to compute RMS from. You can water this down to as slow as you
wish. For human-read meters >2Hz update is too fast afaik.

Peter

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