🚀 go-pugleaf

In article <1992Dec15.161155.4773@fccc.edu>, stodola@orion.fccc.edu (Robert
K. Stodola) wrote:
> 
> This is probably a FAQ question, but...
> 
> When I first put up NTP (a long time ago), I noted that Bell of PA time was
> two seconds faster than my computers time.  Today its off by the same two
> seconds.  One of them is obviously very reliably wrong (I lean towards
> Bell).  It does seem rather curious, especially since its fast rather than
> slow, which might be explained by other types of delays.
> 
> I know the phone company would probably tell me that in a disagreement between
> reality and Bell, they are definitive, but if anyone has an explanation of
> this phenomena, I'd like to hear it.
> 
> -- 
> 
> stodola@fccc.edu -- Robert K. Stodola (occasionally) speaks for himself.

Welcome to the wonderful world of highly accurate time!  The
Internet document RFC 1305 -- which defines Network Time
Protocol -- has an extensive discussion of the things that
can go wrong with time services.  Yale's campus network time
server frequently drifts a bit, too -- right now it is off by
about 1 second.  Local phone companies can be even worse.

Personally, I rely most on my el cheapo wristwatch, which
I *know* gains about 0.093 seconds per day.  I check it
fairly frequently against the NIST clock (available on
various frequencies with a shortwave radio, or you can
phone 303-499-7111).

About once a week I do a linear regresion of error versus
day of the year for the past 6 months, discard all values
that are off by more than 0.6 second, and recompute the
regression line.  This way I am confident I always *know*
the time to within +/- 0.25 second.  Theoretically computers
"should" be able to do better than 0.25 second, but I've yet
to encounter any that do.

[for those who may be curious: It is a CASIO F-24W for which
 I paid 15 dollars ca. 5 years ago.  I have never even replaced
a battery, and it has never to my knowledge deviated significantly
from the 0.093 second per day rate I quoted above.  The
packaging claimed the lithium battery was good for 7 years.]


Matt Healy
"I pretend to be a network administrator;
 the lab net pretends to work"

matt@wardsgi.med.yale.edu