Thanks for the links. Indeed if the synchroscope needle is turning clockwise I know the grid frequency is greater than 60 and if counter clockwise then less than 60 and exactly 60 no movement of the needle at all.

To me there is something about watching the inertia of the entire system change and it controlling itself to stop frequency excursions and then AGC or other human interventions to restore the balance.

Thanks for the ideas and links.