How is the exact time figured out for all of the world. Then, in Greenwhich, England is the Master Clock?

Question

How accurate is it?

Answer 1

Start at the first reference for more detail than you can imagine. The better references are kept synchronized within 100 nanoseconds.

If it's for business rather than science, UTC is much more commonly used, see the second reference.

Answer 2

on the railroad we use universal coordinated time , its from U.S. navel observatory in Fort Collins Colorado . i believe they now use an ion cascade fountain clock . most time is based on an astronomical year , approx. 365 days 6 hours 24 minutes .