While a coil is being wound, it is a simple matter to count the turns by any simple form of revolution counter.
In the machines they were accustomed to there was nothing but a revolution counter, and sometimes, though not always, a compass.
Besides, the pulley shaft actuates a revolution counter, and a clock measures the time employed in the experiment.
I had nothing to do other than to give occasional attention to the revolution counter, altimetre, and speed-dial.
The addition of a revolution counter to the drum, then, will solve the problem.
The watch, anemometer and revolution counter were all automatically started and stopped simultaneously.