Wow, so much good info, thanks all!
@RVDT - "Flyweight governors have inherent droop - this gives stability to stop it hunting incidentally. "
This was the fundamental point I was missing. I had heard this but didn't understand it, I thought the governor was designed to return to the previous speed. You're saying that it can't do this without causing hunting and is inherently designed to give up some of the original speed.
"Droop occurs because the spring tension is non-linear"
I'm not quite grocking this yet. I see how a basic droop arm works to modulate the spring tension, but not how the conical speeder springs result in droop. I'll keep trying...
"The beep trim is there to compensate for atmospherics - the P in DP N1/N2 is a pressure which varies from day to day"
This point, (and the similar points made about leaving the INCR/DECR alone) is very illuminating; as I've just been on the receiving end of "DECR on downwind and INCR on final". And the related point about not creating a failure opportunity at a remote sight.
@wrench1 and PEASACAKE - I probably don't need to know the internal details. I think you're right that I'm trying to understand how to use it, by understanding how it works. These replies have helped a lot.
THanks!