high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid, aatomiaja skaala, mille puhul aja mõõtmine põhineb elektromagnetvõnkumistel, mida kiirgavad aatomid siirdumisel ühest energiaseisundist teise, scale that is computed by taking the weighted average of more than 300 atomic clocks, and these clocks are located at more than 60 timing laboratories around the world