[timf]

Well, quoting from: http://www.eecis.udel.edu/~mills/ntp.html

"Used in the Internet of today with computers ranging from personal workstations to supercomputers, NTP provides accuracies generally in the range of a millisecond in LANs and up to a few tens of milliseconds in the global Internet"

But this is news to me, interesting:

"When kernel support for precision timing signals, such as a pulse-per-second (PPS) signal, is available the accuracy can be improved ultimately to the order of one nanosecond in time and one nanosecond per second in frequency."