I'm curious: what's the use case for microsecond-precise timekeeping?
I could have used an in-between time unit, like hundredths of a millisecond, but that would have created embarrassingly long variable names.
What's the use case for microsecond-precise timekeeping, that is of interest to (i.e., benefits) FB?
But, by no mean, does it mean we use special timing - but now that I say that, I realize I have no clue where our time signal comes from, clearly it wouldn't be the internet because our trading servers aren't exactly directly connected there, we must have an internal ntp sever o_O
Imagine super high speed, high precision robotics, maybe a synthetic fiber layup machine or an exotic milling machine, that moves at 10m/s. If you have 1us of precision and accuracy then you can send movement commands that are precise down to 10um.
An example that does - I work for IceCube, a big neutrino detector at the South Pole. The detector is essentially a time of flight system that detects emitted light as it propagates through the ice when a neutrino interaction happens. We need good time distribution in the system so we can marry up hits from the 5000 odd sensors in the ice (and successive hits may be nanoseconds apart), and we need good absolute precision because we collaborate with other observatories.
Also pretty much all radio telescopes that do long baseline interferometry need excellent absolute timing. The South Pole Telescope has (I think) the most accurate clock on station, a hydrogen maser-based system. We use GPS.