Tg is a timegrapher program: a software used to regulate mechanical watch movements and evaluate their performance. Tg detects the noise produced by the mechanism of a watch, analyzing that noise it computes real-time readings of the rate (i.e. how fast or slow the watch runs) and other operational parameters (beat error, amplitude).
Tg is in development, and there is still no manual. For more info on tg see https://github.com/vacaboja/tg and this thread at WUS. In particular, the calibration procedure is described at this post.