If you have a beat counter, it's a fairly simple process to let it count while the minute hand rotates one full turn (exactly) around the dial. The accumulated beats will be your beats per hour. You don't even need the pendulum on it if it will run without it. For more accuracy, let it go two or more times around, and divide the total by the number of rotations.
I try to make it a rule to count the wheels while apart
but times I still forget while busy thinking about the problem
Knowing better and doing better are two different things.
It can be done from the edge of an assembled clock, marking the wheels
with a sharpie every 5 teeth, as it runs. The marks can be cleaned
with solvent later. Use 2 dots for the first mark.
The harder part is the pinions. I get tricked on 6 or 7 teeth.
Either way, it is a pain.