What is it? Set 385

77.92 RPM could also be called official. As of 1925, records were recorded without electric motors because line frequency was not considered steady enough. Record players were adjustable because different producers used different speeds, from 74 to 82 RPM.

In 1925, Bell Systems began making electrical recording equipment. Bell went with 78 because that's what Victor, the biggest producer, used. Rubber wheels wouldn't have been precise enough, but a worm gear would give them 78.26.

The same year, Bell Systems set the 33-1/3 RPM standard for cutting records to play with movies. Movies soon went to other technology.

45s and consumer 33-1/3s came out after WWII. They were probably chosen because they are exact factors of synchronous speed and are easier to remember than 78.26.

Equipment for 50 Hz uses 77.92.

What we really need is a recording of "Never Gonna Give You Up" played with one of these things. First, it's a real rickroll. Second, it would do damage to the recording, which can only be a good thing :-)