Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!nprdc!trejo
From: trejo@nprdc.arpa (Leonard J. Trejo)
Newsgroups: comp.lang.c
Subject: PRECISE TIMING ON IBM PC/AT COMPATIBLE
Message-ID: <2924@arctic.nprdc.arpa>
Date: 20 Jul 89 21:39:07 GMT
Sender: news@nprdc.arpa
Reply-To: trejo@nprdc.arpa (Leonard J. Trejo)
Distribution: usa
Organization: Navy Personnel R & D Center
Lines: 21


Say, we're trying to measure human reaction times (<1ms) by timing the
interval between a video field and a keypress (on the keyboard) on 
our PC-compatible (Compaq 386/25) using the C subroutine call 
"ftime()", which purports to provide millisecond accuracy (MSC 
5.1).  Some net-news discussions I've followed say that the 
precision of ftime() may actually be _worse_ than 1 ms (say 8 ms), 
even though the time returned is measured in ms.  So, I thought I'd 
ask to see how others accurately measure intervals on PC's.  Would 
you be kind enough to send me a short description of how you do it 
and/or some example programs?

			L. J. T.

============================================================================
ARPANET : trejo@nprdc.navy.mil		UUCP:  ucsd!nprdc!trejo

U.S. Mail: Leonard J. Trejo, Ph. D.	Phone: (619) 553-7711
	   Neuroscience Laboratory		(AV) 553-7711
	   NPRDC, Code 141
	   San Diego, CA 92152-6800