Sometimes the numbers on the gear are teeth count numbers, and you just divide.
If you are looking at the ring gear just count the teeth on that and the pinion, and divide, this is the most accurate method.
If you want to count turns, turn both wheels at the same time 10 turns, count pinion turns, then divide pinion turns by 10, this will be close.
Or turn one wheel 20, hold the other, and divide pinion turns by 10, close again.
Grigg
