21 May '20 22:25>
Making 10Ghz microwave sources near as accurate as an optical clock, which is like one second in ten billion years off, something like that.
https://phys.org/news/2020-05-scientists-boost-microwave-stability-hundredfold.html
https://phys.org/news/2020-05-scientists-boost-microwave-stability-hundredfold.html