Path: utzoo!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!ucbvax!ucsd!nprdc!nebeker
From: nebeker@nprdc.arpa (Del Nebeker)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Turbo Pascal 5.0 and GetTime
Summary: Timing on PC's
Message-ID: <1187@arctic.nprdc.arpa>
Date: 16 Dec 88 16:09:10 GMT
References: <45782@yale-celray.yale.UUCP>
Sender: news@nprdc.arpa
Reply-To: nebeker@nprdc.arpa (Del Nebeker)
Organization: Navy Personnel R&D Center, San Diego
Lines: 30


 We have been doing psychology experiments with a similar intent for about
three years.  We have been capturing keystroke counts  and times while in
dBase tasks.  We had to write an Assembler program that would monitor the
keyboard and store the count of keystrokes and the elapsed time and then
deliver those register totals to another program after the timing was 
complete.  

We found that on the XT the best resolution possible was based on the clock
tick rate.  That is, any instruction or execution of an interupt was paced
by the pulse of the internal clock rate.  In the XT this rate is 18 times
per second at least as the far as the keyboard is concerned.  That translates
into resolution of .0556 seconds.  Therefore
if the event is occuring in less time than this it will not be timed accurately.

Even if the event is longer than this there will also be some error not to 
exceed .0556 second.

I can't speak  to any other Machines but I'm sure the logic would be the
same.

I hope this is of some help.  If anyone else has a better explanation I'd
like to know about it too.

Del Nebeker
Code 161
Navy Personnel R&D Center
San Diego, CA 92152-6800
(619) 553-7749
nebeker@nprdc.arpa