TAhanks for that link which fits with my measurements (nowhere as detailed) of ones actual ability to do things with "modern" hardware. In the 1980's I was used to being able to measure events with 0.2 microsecond precision using a PDP-11 and my expectation was that the accuracy was only going to improve as processors got faster. I ported a program I wrote on the PDP-11 to a Commodore 64 in 1988 and was using it to measure finger tapping with a switch array to 1 msec accuracy. This was done through the simple expedient of speeding up the sample rate for the keyboard to 1 KHz and the adding in my 4 external switches as "keys". Used a 512 K Mac to get the serial data and display results. To do the same now would require custom hardware to do the timing and a USB link to a "modern" CPU or implimentation on a microprocessor When I attempted to get this same type of timing accuracy from a PC, found out that it was no longer easy to get access to interrupts as easily as before and keyboard latency was longer as now keystrokes were detected by an on board microprocessor and sent out as a series of packets for each keystroke. In DOS and W95 where one could still easily get at interrupts, then a serial port could be used to do msec timing. Once XP and beyond arrived, then the best temporal precision one can expect from a 3 GHz machine is 15 msec. I suspect the same holds for Macs and haven't tried running real time Linux as I either pull out my trusty C64 from time to time and use it for precision timing (unfortunately have only one copy of the code on casette tape so when that goes can't do this anymore) or I use various microprocessors to do the job. Have a nice microsecond precision timer that I wrote for a Propeller chip and feel much more comfortable programming for it than the latest windoze bloatware system. The Propeller has the same amount of RAM as the PDP-11's I started on, runs 20x faster/core and is fun to program. The microsecond timer is attached to a geiger counter to generate random bytes for OTP encryption. Boris Gimbarzevsky