Hey Mark, Thats how we all learn, that looks to be a “fast slow regulator” by turning the thumb wheel that sticks out thru the dial it lengthens or shortens the acting part of the suspension spring, this will lengthen or shorten the pendulum, effecting the rate of the pendulum oscillation. The suspension spring would hang on another slotted “fork” and thru the one in your picture. Hope that helps, Have fun, William