International Atomic Time

And just over a decade later, in 1967, the body overseeing the International System of Units convened for their semi-regular General Conference on Weights and Measures, where they redefined the length of a second according to Essen's definition.

This enabled the establishment of extremely precise International Atomic Time, and eventually Coordinated Universal Time, which combines the reference point of Greenwich Mean Time with atomic levels of accuracy.

By then, the most precise atomic clocks were not gaining or losing a second in over 30,000 years.

And within only a decade, this margin had been stretched further to some 400,000 years.