Activity

NIST’s Aluminum Ion Clock Set A World Record In Accuracy, Measuring Second To The 19th Decimal. A 2-Mile Laser, Magnesium Ion, & Titanium Chamber Make It 41% More Precise, & 2.6× More Stable Than The Previous Best, Strontium 1. It Beats Cesium Clocks, The Gold Standard For Second, Advancing Quantum Physics & Redefining Time By The Second.

https://www.popsci.com/technology/most-accurate-optical-atomic-clock/

It measure a second down to the 19th decimal.