Metre Convention
The atomic clock has made very precise time-keeping possible. The earth is slowing down. A the "time of the dinosaurs" the earth rotated once every 23 hours. It is now possible to measure variations in the Earth's rotation caused by volcanoes and tsunamis. This is done by the International Earth Rotation Service (IERS). The IERS  proposes leap seconds as and when these are needed.  Under the Metre Convention, the BIPM has the task of coordinating over 200 atomic clocks around the world. These clocks are located in 50 different national laboratories.