A watch timing machine or timegrapher is a machine that acoustically measures the ticks of a mechanical watch to assess its accuracy and enable calibration. This device calculates the amplitude, beat rate, and beat error of a mechanical watch, and provides a summary of these figures after the watch is connected to the device for a fixed interval of time. The information recorded by this instrument is used by horologists and watchmakers to help determine if the timepiece's movement is in need of servicing, or a complete overhaul, to restore its timekeeping accuracy. It is also used to determine if a newly produced timepiece is accurate, prior to being sold or released.
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Wikimedia Commons has media related to Watch Timing Machines.References
https://millenarywatches.com/best-timegraphers-for-your-watch/ Millenary Watches: How does a timegrapher work? https://millenarywatches.com/best-timegraphers-for-your-watch/ ↩
https://www.bobswatches.com/watch-resources/how-to-use-a-timegrapher Why You Should Own A Timegrapher (and how to use it) Bob's Watches, JANUARY 07, 2015 https://www.bobswatches.com/watch-resources/how-to-use-a-timegrapher ↩