When they did the gun reaction tests many years ago, the actual fastest reaction time recorded was something like .115 . But they rounded it down to .10 just in case there was an outlier somewhere who had a reaction time that was legitimately faster than .115 .
The reality is that many runners whose reaction time is between .10 to .109 are actually anticipating the gun, not reacting to it.
The rule is ridiculous. The reading relies on force plates, probably piezoeectric, in the blocks—and HOPEFULLY some kind of algorithm, not just some instantaneous threshold, or windowed summation.
The problem is that people twitch in the blocks involuntarily, and not only can it not enhance their start, sometimes it makes it worse. And different people apply different basic back-pressure.
The 0.010 should only be used as justification for a closer look at the tape, but that’s not how it’s done. Bad rule.