It is very attractive to use the world-wide Internet links for time sourcing.  Indeed, many simple programs are freely available that will set computer clocks to standard time, but for most users the end result may only be accurate to about one seconds.  This is caused by a number of problems:

• Modern operating systems have NTP synchronising modules built-in and they can be set to regularly check the PC clock. For older operating systems small programs are widely available that perform this same task
  
• Home Internet conections are getting faster, the Internet world-wide is increasing in capacity, but the Internet is by design not a "direct line to the time server".
  
• Many users will access the Internet with a browser on a PC running a form of the Windows operating system.  The internal timing and task sequencing procedures in older (95, 98) versions of Windows are event driven and not designed to enforce accurate timekeeping.  We are told that other versions (NT, XP) are better in this respect (?), as ara various flavours of Linux and Mac.
• Generally, faster computer hardware, when not burdened with numerous parallel tasks, should be able to perform jobs more swiftly, including keeping time.
  
• The Internet is a wildly flexible system where messages can be ‘routed’ in many different ways following short or long or very long paths, causing unpredictable, variable network delays.  While the time setting programmes make an effort to measure - and correct for - these network delays, they do introduce significant uncertainties.  To confirm this for yourself: please run of of these popular programmes repeatedly a few times and note the great variation in the "results".
• To complicate things, most PCs have two clocks on board  (see the 'Synch' discussion here),  and these are normally not synchronised.  Further, the CMOS clocks on many motherboards runs significantly day fast or slow, so that they will drift away fairly soon after having been ‘set’.

"On most Win 3x, 9x, 2000 and ME systems, the time cannot be set more accurately than to the nearest second.  It is therefore possible that the time of your system can be wrong by up to +/- 0.5 seconds even immediately after you adjust your clock based on data received from one of the NIST servers.  In addition, the clocks on many computers can gain or lose several seconds per day, so that even a clock that is set correctly will not stay that way for very long.

Windows NT  (and XP)  have more sophisticated software support for the clock, but the hardware is usually not any better.  If your application requires that the time on your system must be correct to within +/- 1 second at all times then you will probably only be able to achieve that level of performance using Windows NT and a continuous connection to the Internet.  ................., and you may find that even Windows NT does not completely satisfy this requirement..........."

THERE ARE A NUMBER OF OTHER, EXCELLENT WEB SITES:

• Very informative site  NTP Public Time Servers by David Mills  with many good links.
• Further interesting discussion in the Help file of the program  AboutTime.
• Also interesting discussion on the site of the program   Socketwatch.
• There are many other similar programs, but please read the background material carefully and appreciate the advantages and limitations of these methods.  If at all possible, check the performance against another - independent - source of known accurate time.
• Tardis  is another suite of programs recommended by users.
• Refer to the review articles in  Windows and Net Magazine

There are services available in most countries to set computer system clocks through Internet links to standards laboratories.  For professional computer users (e.g. banks, mainframes), this is a normal part of life.  It is worth reading the  NIST summary on "Set Your Computer Clock Via the Internet.  For example, there is a   TimeServ program included in the Windows NT Resource Kit.   For individual home users this is in principle also possible, but the result depends very much on the particular computer configuration and the operating system being used.  Even then, achieving an accuracy better than 0.1 second is far from easy.  These are issues that need to be worked out with specialists.

NEW ZEALAND:
The New Zealand Measurement Standards Laboratory  advises the following about the 'MSL Time Set Service':   "A computer readable time code is available through the telephone network.  The service is available on 0900 45222. Programs are available (free) from MSL to access this service from Window 3.1 and Dos computers. For Windows NT computers we recommend using the TimeServ.Exe program which is available as a part of the Windows NT 4.0 Server Resource Kit. This program supports the MSL dial up system.  For other operating systems, you are on your own."