In 1976 a new state primary time and frequency standard of the USSR was certified and confirmed with an error of reproducibility less than 1 × 10−13 and with an unavoidable systematic error less than 3–4 × 10−13. This standard includes a laboratory primary cesium beam frequency standard providing an independent definition of units in the SI system, primary hydrogen frequency standards preserving the units of frequency and time intervals, and hydrogen and cesium clocks providing the TA(SU) and UTC(SU) time scales.