78 rpm speed
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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 60 Hz it was 78.2608696 rpm, the speed of a 3600 rpm synchronous motor reduced by 46:1 gearing. For countries with 50 Hz it was 77.9220779 rpm, the speed of a 3000 rpm synchronous motor reduced by 77:2 gearing.