Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!gatech!rutgers!att!ihlpf!gmark
From: gmark@ihlpf.ATT.COM (Stewart)
Newsgroups: comp.sys.att
Subject: Re: 3b1 real time clock runs fast
Summary: cron
Message-ID: <7657@ihlpf.ATT.COM>
Date: 10 Feb 89 00:42:31 GMT
References: <671@gvgspd.GVG.TEK.COM>
Distribution: na
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 27

In article <671@gvgspd.GVG.TEK.COM>, mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) writes:
> I have found that my 3b1's real time clock gains about a minute per week, and
> was wondering if any of you hardware types out there might be able to steer
> me toward a trim cap or something to correct this annoying, if not monumental,
Actually, a simpler way to do this (my opinion) is to just look in
crontab and modify the job that updates the display and have it
reset the time.  Write a simple program that takes the time you
type in at one-week or even one-month intervals that you consider
correct and calculates the deviation of the date stored over that
period.  In other words, you type in a time, program checks if it
agrees, and if not, checks the last time it was updated (timestamp
on a file you created at the last update) and figures the percentage
deviation.  Putting this percentage into a file, modify the crontab
file to not only update the display, but to update the time setting
by this percentage each time, or a separate entry to fudge it
every day or week or so.  This has the advantage of being dynamic
and correcting for things like thermal fluctuation (I don't know
how significant that is on the UNIX-PC).  I have found that
all the UNIX-PCs I know about have positive deviations.  Do 
others find that's true?  Maybe they run hot?  


				- Mark

				G. Mark Stewart
				ATT_BTL, Naperville, Ill. ix1g266
				ihlpq!gms (312)979-0914