AND AUSTRALIA TIME RESOURCES
If you can help us with additions, corrections, new links, please
The address is on the NZ&A Time home page.
1. Using the Internet (accessed by cable, phone line, Wi-Fi or
2. Using a direct Telephone link to a time server without
VERY CONVENIENT TO SET COMPUTER CLOCKS
TO WITHIN ABOUT A
UTC - WITH THE RIGHT HARDWARE AND
OPERATING SYSTEM YOU MAY DO BETTER THAN THAT
Could Apple MAC users perhaps advise us on
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
about one seconds. This is caused by a number of problems:
Some real life experiences:
- 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
- Home Internet connections are getting faster, the Internet
world-wide is increasing in capacity, but the Internet is by design not a "direct line to the
- 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
event driven and not designed to enforce accurate timekeeping. We
are told that other versions (NT, XP) are better in this respect (?),
as are various flavours of Linux and Mac.
- Generally, faster computer hardware, when not burdened with
parallel tasks, should be able to perform jobs more swiftly, including
- The Internet is a wildly flexible system where messages can be
in many different ways following short or long or very long paths,
unpredictable, variable network delays. While the time setting
make an effort to measure - and correct for - these network delays,
do introduce significant uncertainties. To confirm this for
please run of of these popular programmes repeatedly a few times and
the great variation in the "results".
- To complicate things, the crystal clocks
on many motherboards run significantly fast or slow, so that they
drift away fairly soon after having been ‘set’.
- Modern fast PCs, hooked up to a broadband connection, using a
good quality NTP synchronising program, can typically set their clock
to a few tenths of a second. For example, in XP, the "Adjust Date
and Time" > "Internet Time" function does this well. You can
set the time manually "Internet Time" and click the "Update Now"
button. You can
adjust the regular automatic synchronisation interval by changing the
setting "SpecialPollInterval" in the "NTPClient" Registry key from the
default value. Do a Google for more details or check e.g.
NOTE that under XP this adjustment can only be made if you have
Administrator rights. If your XP computer only has one "User",
this will be the case.
- Alternatively, the program
by Paul Lutus also does this nicely (in 95, 98 and XP) and can easily
be set to synchronise at any chosen interval (even as short as parts of
a minute (e.g. enter "0.25"
minute). NOTE that under XP this program only works if you have
Administrator rights. If your XP computer only has one "User",
this will be the case.
- Make sure the computer is only 'lightly loaded" and not doing too
much multitasking in the background. Check that only one
"User" is active and that this user has "Administrator" rights.
Do not add fancy artistic smart designs to the clock.
- You have to know the clock in your PC to estimate what minimum
synchronisation interval is required to keep clock drift below a chosen
level. This will also change with temperature; in this case the
temperature at the location where the crystal is mounted on the
motherboard. To estimate the drift rate disconnect your PC from
the Internet, run it for a few hours and
check the time against another independent source, like WWV(H).
- The next BIG question is: how do you extract the time from the
PC. If you want to "Look" at a digital clock, the default XP
clock does not show seconds. However a small program
"TClockEx" by Dale Nurden will display a pretty accurate clock
with seconds display, replacing the default XP clock. Version
1.4.2 of TClockEx works well in Windows 98 and XP.
- WARNING: some clock display programs available on the
Internet do NOT provide an accurate clock display. For example
the program "Sync-It with Atom" presents on the screen a
digital clock with second display which (on some systems) can be off
the correct time by as much as a full second. This is a serious
warning to us all to not always believe the description of smart
looking software. Be warned.
- From experimenting with Ubuntu Linux distributions (now at 8.10),
the default built-in clock - which shows seconds - "appears" to work
well at boot time, even on somewhat older computers. NOTE
that on some systems you have to first install NTP support.
People familiar with the operating system can also change the
synchronisation interval for this to maintain synchronisation over
time. Of course, before you
believe anything to be 'true', do take note of the ADVICE below.
- ADVICE: whatever
you choose to work with, it is
essential to calibrate this against a source of known good time, like
WWV(H). PCs come in a bewildering variety of hardware an drivers
and there is no one recipe that works for all. We cannot
guarantee that what works on your "Brand X" machine will also work on
another "Brand Y" computer....!
Please read the information at the web site of NIST (the US National
Institute of Science and Technology, formerly the NBS, National Bureau
of Standards) NIST summary on
"Set Your Computer Clock Via the Internet. It is also
strongly recommended to download and run the public domain NIST - TIME
software, available at that page, and read the Help files and the
excellent 21 page PDF file associated with this. The Help
files provide information on the limitations of setting computer clocks
and read in part:
"On most Win 3x, 9x, 2000 and ME systems, the time cannot be set
accurately than to the nearest second. It is therefore possible
the time of your system can be wrong by up to +/- 0.5 seconds even
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
+/- 1 second at all times then you will probably only be able to
that level of performance using Windows NT and a continuous connection
THERE ARE A NUMBER OF OTHER, EXCELLENT WEB
QUESTION: does anyone know of
reliably good methods?
- Very informative site NTP Public Time Servers by
David Mills with many good
- Further interesting discussion in the Help file of the
- Also interesting discussion on the site of the
- 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
is another suite of programs recommended by users.
- Refer to the review articles in Windows
and Net Magazine
Please contact us.
COMPUTER CLOCKS BY TELEPHONE
WITHOUT USING THE INTERNET
There are services available in most countries to set computer
clocks through Internet links to standards laboratories. For
computer users (e.g. banks, mainframes), this is a normal part of life.
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.
individual home users this is in principle also possible, but the
depends very much on the particular computer configuration and the
system being used. Even then, achieving an accuracy better than
second is far from easy. These are issues that need to be worked
Measurement Standards Laboratory advises the following
the 'MSL Time Set Service': "A computer readable time code
available through the telephone network. The service is available
0900 45222. Programs are available (free) from MSL to access this
from Window 3.1 and Dos computers. For Windows NT computers we
using the TimeServ.Exe program which is available as a part of the
NT 4.0 Server Resource Kit. This program supports the MSL dial up
For other operating systems, you are on your own."
Telstra operated (until about 2005??) a
"Computime" service to set computer clocks. An
archived article in Windows
and Net Magazine (Dial Up) gives some references on this
and many other dial up services all over the world. Not sure if
this is still active. The CSIRO National Measurement Laboratory
may also still provide this service.