That PS Audio tutorial on setting VTA is somewhat helpful to the extent it provided an explanation of how records are cut:
"The object is to match, as closely as possible, the same VTA as the original cutting head for the master was set. Typically, there is an easy standardized method - that relates to the degree of angle used by almost all cutting masters. The Vertical Tracking Angle was not always standardized. But since the stereo disc was launched, the angle was defined at 15 º and was changed in the nineteen seventies to 20 º. That is why the Ortofon SL-15 became SL-20."
Where this explanation errs is the assumption that, in practice, there was standardization - there wasn't, and swings of plus or minus 10 degrees from the various standards were common. In fact, I know of a presumably gold standard CBS test disc used for setting up cartridges whose azimuth was off by 15 degrees. I will repeat this - the cutter head is set individually for every side cut. Each individual side thus has its own unique VTA and azimuth. To set VTA correctly for each side, you can either listen or measure distortion - in practice, record thickness has no bearing, none, on the angle that the grooves are sitting in the record.
"The object is to match, as closely as possible, the same VTA as the original cutting head for the master was set. Typically, there is an easy standardized method - that relates to the degree of angle used by almost all cutting masters. The Vertical Tracking Angle was not always standardized. But since the stereo disc was launched, the angle was defined at 15 º and was changed in the nineteen seventies to 20 º. That is why the Ortofon SL-15 became SL-20."
Where this explanation errs is the assumption that, in practice, there was standardization - there wasn't, and swings of plus or minus 10 degrees from the various standards were common. In fact, I know of a presumably gold standard CBS test disc used for setting up cartridges whose azimuth was off by 15 degrees. I will repeat this - the cutter head is set individually for every side cut. Each individual side thus has its own unique VTA and azimuth. To set VTA correctly for each side, you can either listen or measure distortion - in practice, record thickness has no bearing, none, on the angle that the grooves are sitting in the record.