Yep - and with Cesium, the on-board clocks would always be right....
and with Cesium, the on-board clocks would always be right....
Not exactly, kind of sort of.
The time dilation thing, kind of creeps up on you.
Cesium Beam atomic clock units used in the Hafele–Keating experiment.
And the whole project was checked by a stewardess with her Timex. See photo at link.
https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment