Atomic Clock Sync with NTP
Sync you PC with a atomic clock.
Easy and at least more accurate than a PC clock. It uses the "Time protocol"
rfc868.
Atomic Clock Sync with SNTP 

3d Traceroute PRO allows to use SNTP (instead of the older "Time Protocol").
It is more precise. Additional you can query a public available list of Stratum
2 and Stratum 1 time servers.
Additional it can query multiple server. With multiple servers the accuracy
of the result can be tested. 3d Traceroute looks for adjacent clock errors
within a certain limit. Clocks outside this limit are rejects. The avarage
is then used to set the clock.
By doubleclicking a row this server can be used as time server.