[time-nuts] Time syncing question

Bill Hawkins bill at iaxs.net
Tue Aug 29 20:04:16 UTC 2006


What a marvelous range of answers this topic has produced.
Perhaps it is the blind men and the elephant, again. Here
are some of my blind observations:

1. Experience logging industrial process values taught me
that it is most important that time be monotonically
increasing. How would you plan to handle daylight savings
time? Leap seconds? Is there a time when the device is
certain to be idle? If so, you do not have an international
business. What are the consequences of not having steadily
increasing time, in your application?

2. There have been some wild guesses about the telco time
error rate and direction of change. I have an AT&T Caller
ID device which shows time of day and corrects it every
time a call is received. This implies that the telco has a
pretty good idea of the time of day, as well as frequency.
Also have an AT&T 7720 cordless answering machine which is
not set but gains 10-15 seconds per day. YATS32 tells me my
computer gains 5.3 seconds per day. What we need is the
expected drift rate of the telco device and the tolerance
you have for absolute drift. I reset my answering machine
every 3-6 months. I can always calibrate the difference by
pressing the Clock button and hearing its current time.

3. We do not know exactly how the telco device time can be
set, or if time can be read from the device.

4. If you elect an elegant solution (if one exists) who will
pay for it? I assume this is a business application and not
a hobby that we are talking about.

Does this shed any light on the problem? Or are we blind men
wearing coarse gloves.

Regards,
Bill Hawkins





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