Oh please--you have to be kidding. I can easily see if a ball bounces a little more than 1/2 way back up when I drop it--besides it's easier just to squeeze them to tell if they're dead or not. You have WAY too much time on your hands--maybe you should spend more time actually playing tennis.
do you take into account humidity and air density? altitude above sea level and its effect on gravity? your latitude and the inertia produced as a result of earth's rotation? Also in play would be the counter gravitational pull of the sun and moon depending on their position relative to earth's orbit and the time of your ball test.
My guess is you're just winging it and it's holding you back from true GOAT.