[ntp:questions] Re: Naval Observatory Master Clock
Brad Knowles
brad at stop.mail-abuse.org
Mon Jul 11 00:47:18 UTC 2005
At 11:17 PM +0000 2005-07-10, David M. Alexander wrote:
> I plan on using it to calibrate timers for work. My device used to
> calibrate the timers must be traceable to a NIST standard.
NIST doesn't set the standard for time. That's an international
standard, called UTC. NTP is designed to keep the clock of your
computer as closely sync'ed to "true" UTC time as is possible with
the particular hardware/OS/software configuration you have, and some
configurations are capable of better accuracy than others. But
they're all going to have a certain amount of error. You'd have to
determine what level of error is acceptable.
Whatever method is used by your upstream time servers, they
should all be traceable back to UTC. They could use GPS, CDMA, GSM,
radio waves broadcast over stations like WWV/WWVB/WWVH or DCF77, or a
variety of other techniques. You would need to look into the various
types of reference clocks (refclocks) and see which ones would meet
your requirements for traceability and accuracy.
> Right now I have
> to call a long distance number and listen for 1 minute, then call again at
> 15, 30 minutes and again at 24 hours.
That's another type of refclock.
> Was thinking if I could just use a
> function or a macro in excel that would get the time in UTC, GMT or Zulu I
> would have to call.
You could use NTP to keep the time of your system within your
required levels of accuracy, and then you can use whatever Excel
macros you want to take the time stamp from the system clock.
However, keep in mind that Windows has some internal issues that
tend to keep it from being able to keep very good time. There are
also hardware/firmware issues which may make your life even more
difficult.
Using NTP with a suitable configuration is going to be the best
you can do, but there are still a number of activities that occur on
the system which will block out clock interrupts while they are being
done, and they will play hell with your time stamps and your time
calculations.
Depending on your particular standards for accuracy, you may well
be better served by choosing a different OS, and you may need to use
different hardware to run that OS. It's all going to depend on just
how accurate you have to be.
Regardless of OS, some hardware is so far out of whack that you
just can't keep it in sync. Keep that in mind.
> The spreadsheet could do the calculations to see if the
> timers met the requirements. I have been to web sites that displays UTC so
> figured that there must be a way to get it and place it in a cell.
There's no magic here. Use NTP to keep the system clock within
the levels of accuracy you require, and then use all the standard
Excel (or whatever) features that you're used to.
Of course, if you have to run a different OS in order to achieve
the levels of accuracy you require, then you will need to come up
with different processes to do the measurements and then transfer
that information to your PC where you can run the necessary
spreadsheets.
> The reason I would like to place the time in a spreadsheet is so I can
> create a certification for audit purposes.
Of course, anything could be put anywhere on the spreadsheet.
The value is not in the numbers, the value is in the person who makes
particular claims about how they got to the numbers and how much you
trust them to have actually used that process.
You should read some of the documentation at
<http://ntp.isc.org/bin/view/Main/DocumentationIndex>, to get a
better feel for what NTP can do for you and how to make use of it on
your systems.
BTW -- the address you're posting from is totally bogus. The
people who actually own abc.com probably don't appreciate your
mis-appropriation of their property that results from lying about
your real address. That is also a pretty negative reflection on you
and your professional reputation in whatever is your particular field
of work.
Any auditor worth their salt who found out that you were posting
to a public mailing list/newsgroup and lying about your real address
would probably not look very favourably at the result of your work
sitting in front of them.
--
Brad Knowles, <brad at stop.mail-abuse.org>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/> for more info.
More information about the questions
mailing list