The HTTP Time Protocol (HTP) is used to synchronize a computer's time
with web servers as reference time source. Htpdate will synchronize your
computer's time by extracting timestamps from HTTP headers found
in web servers responses. Htpdate can be used as a daemon, to keep your
computer synchronized.
Accuracy of htpdate is usually better than 0.5 seconds (even better with
multiple servers). Htpdate can also work through http proxy.

WWW: http://www.clevervest.com/htp/