Rivets
There is a schematic here:
http://www.petervis.com/electronics%...%20Diagram.gif I've made it a link so you can print it out full size.
You will see that the ac and dc circuitry has been separated, ac on the left and dc on the right. If you care to calculate your way through you will find that there is a 1.11 ratio in sensitivity.
However this is drawing attention away from my point. The AVO8 is not true RMS.