"The Network Time Protocol (NTP) is a protocol for synchronizing
the clocks of computer systems over packet-switched,
variable-latency data networks. NTP uses UDP port 123 as its
transport layer. It is designed particularly to resist the effects
of variable latency (Jitter).
"Using NTP is a great way to keep your system clock set
correctly. It works by contacting a number of servers around the
world, asking them for the time and then calculating what the
correct local time is from their responses..."