Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!ukma!rutgers!apple!motcsd!xdos!doug
From: doug@xdos.UUCP (Doug Merritt)
Newsgroups: comp.sys.amiga.tech
Subject: Re: TICK and J300
Message-ID: <286@xdos.UUCP>
Date: 13 May 89 15:46:06 GMT
References: <3319@hplabsz.HPL.HP.COM> <6854@cbmvax.UUCP>
Reply-To: doug@xdos.UUCP (Doug Merritt)
Distribution: na
Organization: Hunter Systems, Mountain View CA (Silicon Valley)
Lines: 26

In article <6854@cbmvax.UUCP> andy@cbmvax.UUCP (Andy Finkel) writes:
>Normally, the A2000 takes its 1/60sec  (or 1/50) ticks from the power
>lines, which should be fairly accurate.  When you switch the jumper
>to the "A500" position your A2000 then takes its ticks from the
>video. Which is not quite as accurate.

Unless there is something more going on than what you stated, this
is inaccurate. Power line frequencies drift quite a bit, although
the utilities usually take some care to make the drift average out to
approximately zero over a period of time.

Whereas crystal-derived video timing is as accurate as the crystal,
a difference of several orders of magnitude.

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.
	Doug
-- 
Doug Merritt		{pyramid,apple}!xdos!doug	doug@xdos.com
Member, Crusaders for a Better Tomorrow		Professional Wildeyed Visionary

"Of course, I'm no rocket scientist" -- Randell Jesup, Capt. Boinger Corps