I have recently bought a Radio Shack Digital Sound Level Meter. It has a
facility for taking "average" readings over periods up to 200 seconds. I
tried an experiment where I performed an "average" over a set period during
which, for half of the time I turned the noise source off. Instead of
indicating and average equal to 3db below the source power, a drop of around
8db showed up. Obviously it was not averaging power.

Other tests where I varied the sound source power during the averaging
period, showed that the meter was not indicating average db readings either.

If the "average" indicated is not of power, nor of dbs, just what is it?

An explanation would be much appreciated.

Hank