On 2013-12-01 15:52, Attila Kinali wrote:
On Sun, 1 Dec 2013 13:57:56 -0500
"Dale J. Robertson" <[email protected]> wrote:
A unidirectional error of 1/100th of a second would accumulate around a
minute and a half per day. It's been a long time since I laid eyes on a
mechanical pendulum clock. I remember the clock in my childhood home kept
better time than that. ( I became odd very early. I compulsively compared
the clock time to WWV time at least once a day. I had been using the time
service from the phone company. I felt defrauded when I discovered (via WWV)
that the time from the local telco's dialup time service was just a rough
(very rough) approximation of the time.
IIRC 10^-6 was "easily" acheivable with mechanical clocks, with the
best going to 10^-8 or so (timescale IIRC 1 day).
Hi,
Many clocks and watches were tuned for years before being submitted for rating.
Astronomical regulators (accurate pendulum clocks) kept time within .01s/day,
and
were improved down to about 1s/year, with the help of electromagnets, before
being
replaced by quartz oscillators in the 1930s; regulators in other areas were
replaced by electric clocks timed from the grid during that same period.
The best of these had Q ~110,000, with variations in the hundreds of us/day,
better than network synced NTP servers which vary in the low ms.
Mechanical marine chronometer movements are expected to vary only about
0.1s/day.
Quartz wristwatch COSC certified chronometer movements are rated within .2s/day.
Railroad chronometer movements were expected to stay within 30s/week or ~4s/day.
Mechanical wristwatch COSC certified chronometer movements are rated within
+6/-4s/day.
The "Geneva Standard" certifies movements stay within 60s/week or ~8s/day.
The certifications and standards (including ISO 3159) also require drift in
multiple
orientations and across a range of temperatures ~0-~40C should remain constant.
So with 1 PPM ~ 1 s/11.5 day about 1-10 PPM or 10^-5 to 10^-6 range is expected.
Most modern quartz wristwatches will be in this range and be more accurate than
all
but the best, custom mechanical timepieces.
--
Take care. Thanks, Brian Inglis
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