Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!ames!amdahl!oliveb!tymix!antares!doctor!jms
From: jms@doctor.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.tech
Subject: Re: TICK and J300
Summary: 60Hz is more accurate than most crystals
Message-ID: <213@doctor.Tymnet.COM>
Date: 17 May 89 22:40:23 GMT
References: <3319@hplabsz.HPL.HP.COM> <6854@cbmvax.UUCP> <286@xdos.UUCP>
Reply-To: jms@doctor.Tymnet.COM (Joe Smith)
Distribution: na
Organization: McDonnell Douglas Field Service Co, San Jose CA
Lines: 34

>The intuitive way to see the difference is to look at the accuracy of
>an old fashioned analog electric wall clock driven purely by power line
>frequency, versus newer crystal driven digital watches or wall clocks.
>I've never heard of the former being accurate to within a few seconds
>per year, but the latter are.

But just because a quartz clock is capable of being accurate to a few seconds
per {month,year}, it doesn't mean that your particular crystal has been
adjusted to be that accurate.

A much better example is to consider a simple digital clock that is driven
purely by power line frequency (one without battery backup).  Once set,
the time displayed will be accurate within plus or minus 2 seconds after
one day, after one week, after one month, after one year.  That's right,
the error is non-cumulative.  The power companies guarantee that the long
term average is exactly 60 cycles per second, for this very reason.

I set my clocks using WWV as a reference (303)499-7111.  The battery backed
clock on my VCR gains 10 seconds a week.  It is very consistant; after 6 weeks
it is a minute fast.  But the other VCR which counts 60Hz pulses shows no
detectable drift after 6 months of uninterrupted operation.

The clock on my Amiga 2000 is also fast.  What I don't like is that it requires
manual intervention to adjust it.  It's a hassle, removing the top and adjusting
the cap by trial and error.  I'd love to see a self-adjusting battery-backed
clock circuit.  One that has a line frequency input and compares the time of day
from the 60 Hz clock with the time of day from the quartz crystal and adjusts
itself if there is a difference.

-- 
Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@tymix.tymnet.com
McDonnell Douglas FSCO  | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms
PO Box 49019, MS-D21    | PDP-10 support: My car's license plate is "POPJ P,"
San Jose, CA 95161-9019 | narrator.device: "I didn't say that, my Amiga did!"