By 1925, the speed of the record was becoming standardized at a nominal value of 78 rpm. However, the standard differed between places with alternating current electricity supply at 60 hertz (cycles per second, Hz) and those at 50 Hz. Where the mains supply was 60 Hz, the actual speed was 78.26 rpm: that of a 60 Hz stroboscope illuminating 92-bar calibration markings. Where it was 50 Hz, it was 77.92 rpm: that of a 50 Hz stroboscope illuminating 77-bar calibration markings.