The basic procedure is described in this video by perplxr:
I adapted this method a bit and use my ipad to make a slow motion movie which I then check with quick player for the dead points in single frame steps of the balance wheel to determine the total angle and the amplitude. Then I adjust the time graphers lift-angle to match tha derived amplitude.
The slow motion sequence.
Angle is 140°, the other one 170°. I deduct the difference from 360°, equals 330° = 165° Amplitude.