Sorry for the delay, I was getting unexpected results from the moving average and I wanted to make sure it wasn't something I was doing wrong.
But I 'll get to that in a minute.

Al, here's the results of "Mark2" under the same conditions as before.
I haven't changed the voltage calculation for it, so it's still reading higher than normal.
It looks a little different, but still jumps +/- 2 counts fairly frequently.



Now notice the green line in the above plot.
What, you don't see it ... me neither.
It turns out that the Running average is so slow to respond that it's reading is not even on the chart.
Zooming out a bit shows this ...



This was the formula used ...

Code:
RunAverage  VAR WORD

ADCIN  0, ADval
RunAverage = (RunAverage*15 + ADval)/16
I let it run for over an hour and it was getting close, but it still hadn't reached 2.5 volts.
I don't think I'd want to use that formula.