What Is UTC
- Can I sync my datacenter clocks to UTC?
Literally no, but practically yes. UTC is computed weeks after the fact, so nothing on Earth can synchronize to it — and yet a well-built datacenter clock sits a few nanoseconds away. Here is how both of those are true.
- How does GNSS time relate to UTC?
Not one relationship but two: a whole number of seconds you can look up, and a sub-nanosecond prediction that two control loops — one running in minutes, one in weeks — spend their lives maintaining.
- UTC(k), and who defines yesterday
The realizations you can actually reach in real time — and why the laboratories with the best clocks get the most say in what UTC turns out to have been.
- What does "traceable to UTC" actually mean?
It means an unbroken chain of comparisons back to UTC, each with its uncertainty stated. Not a logo, not a certificate, and not a GPS antenna — which is why most systems that claim it do not have it.
- Can I build my own link to UTC(NIST)?
The data you would need is public, free, and better than most people realize. You can build the measurement in a weekend. What you cannot build is the one thing that turns it into a number somebody else has to accept.