Question: How Can I Set My Clock Automatically? A number of readers asked that I reveal how you can make sure your computer’s system clock correct itself by checking an atomic clock over the Internet. Do note that if your clock is radically wrong and continues to be wrong after you’ve set it, your computer probably needs a new clock battery or similar fix.
Answer: Along with the vast number of other protocols on the Internet, the Network Time Protocol (NTP) is used to synchronize the time of a computer with another computer running an NTP server. NTP can provide accuracy to several milliseconds, although the farther away you are from the source of the time (atomic clocks and the Global Positioning System (GPS)), the less accurate your results will be. Of course, this lack of accuracy is meaningless for normal use – I doubt many people other than researchers care about millisecond accuracy.
To use NTP, you need an NTP client program. For the Mac, check out Network Time (which hasn’t been updated for a long time but still works fine for me) and Vremya, among others. For Windows 95, try Tardis95 or AtomTime95, among numerous others. For a more complete list, plus programs for Unix, DOS, Windows 3.1, Windows NT, and Novell NetWare, check out the Time Synchronization Software Web page. There’s also a Macintosh Time FAQ.
Once you’ve downloaded and installed an NTP client, you must point it at an NTP server, ideally one operated by your Internet provider. If your ISP doesn’t run an NTP server, you can use a public NTP server, but respect the fact that you’re a guest on the server. In particular, if you don’t need the highest accuracy, use one of the secondary servers (called stratum 2) NTP servers in the list in the Public NTP Time Servers page.
For more information about NTP in general, check out the Time Server Web page and the Time Service Department of the U.S. Naval Observatory, which includes both historical information and information about future types of clocks. [ACE]