I'm not sure I followed what you were trying to say, but I concede that there's no reason to use a paintball marker to test velocity. If you know the distance a projectile crosses between two switch points, you can use output relays from each switch to start and stop a timer. Then you can calculate velocity by the distance divided by the time. Did you mean error induced by the accuracy of the switch response? That's a point I'd potentially concede with a photoelectric switch.
The timing chips on Doppler devices are, at least, suspected to drift over time (which, if that suspicion is true, could cause them to be less accurate). Can we guarantee that the photoelectric method of measuring distance traveled over time doesn't have the same problems?
The problem is that you are using one device (like the photo electric based shooting chrony that both punkworks and I use) with a % of uncertainty to calibrate a device that has it's own, much higher, % of uncertainty measuring the speed of an object that has an speed with an unknown % of certainty.
Where are your controls? We can conduct the above experiment, then feed all the results (assuming we have enough data) into an ANNOVA and figure out what's going on... BUT, I prefer to run experiments as cleanly as possible.
I don't think that we should rely on anything that uses a timing chip as a control... if we can help it. I suggested dropping a ball from a known height, so we can calculate it's speed at any position on it's fall path given it's distance and rate of acceleration. We can compare the accuracy of a photoelectric device with our, estimated, speed projections and eliminate the possibility of timing chip drift effecting the measured speed (or we could adjust accordingly). This method will, also, give us the added benefit of being repeatable all over the country. Anyone with an object of sufficient density and low surface area could give us data. I could test my shooting chrony in my garage, you could test your handheld Doppler, someone could use a radar gun, etc.
Edited by Troy, 26 September 2013 - 03:01 PM.