This was taken from the August 1964 issue of Meccano Magazine. By co-incidence it is similar to the digit counter of my current pinball machine model.
The operation is fairly simple. A plunger is pressed for a short time allowing the input shaft to turn by half a revolution. A 5:1 reduction to the first reel means it turns by a 10th. There is a 10:1 ratio to the other reel. This is not stepped so the digit on it can be hard to see.
The motor continuously runs and a friction differential allows movement when the plunger is pressed. However the friction differential does not work very well, why not just a friction clutch?