This jig seems like a better option than eye-balling it ¯\_(ツ)_/¯ Nicholas Ryan, Aaron Dubiansky on Hackster.io:

The potentiometer is programmed with two functional buttons and a OLED readout. A button located on the particle board managing the sensor operation will run a code calculating maximum deviation of the wheel as its spun over a 10 second period. This data will be posted to ThingSpeak as a graph to track ones progress is improving the true of the wheel. Another button located on the particle board managing the OLED can be pressed once the wheel is mounted to zero the sensor at the point where the wheel deviates farthest from the sensor (ensuring the wheel always contacts the sensor). As one spins the wheel, the sensor will update every second and provide a readout.

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