Comment by mananaysiempre

The “clock” is in the distributed systems sense—a monotonically increasing integer on all participating machines, and the whole system is wrecked beyond repair if it ever decreases. Any resemblance to physical quantities is purely coincidental.

(Equivalently, a supply of totally ordered gremlins with the ability to obtain a gremlin greater than any you’ve seen, and things blow up if any of them are ever actually incomparable.)

It’s possible to build this atop a GNSS[1], but it’s quite expensive.

[1] https://www.usenix.org/conference/osdi-06/chubby-lock-servic...