Re: Big Outage
"it can't slow down or drift around in the way a pendulum clock "
An excellent summary sir. Although I'd like to add a caveat to the above, "in terms of it's own frame of reference". After all, that's why they need to take into General Relativity into account when calculating the "time" from the counter results from the point of view of the "stationary" observer :-)
Having said that, I would suggest that what you are describing as an atomic clock is actually little more than the pendulum and maybe the escapement. The rest of the gubbins that does stuff to make the counter result useful, when added to the atomic counter bit is arguably when it becomes a clock.