78 rpm speed

By 1925, the 78 rpm was becoming a standard for gramophone records. The exact speed depended on the frequency of the alternating current electricity supply.

For countries with 50 Hz it was 77.9220779 rpm, the speed of a 3000 rpm synchronous motor reduced by 77:2 gearing.

For countries with 60 Hz it was 78.2608696 rpm, the speed of a 3600 rpm synchronous motor reduced by 46:1 gearing.