If by chance measuring racquet tension with either the Gamma STT (String Tension Meter/red and black one) or the Tourna String Meter (black one), I'd put zero bets on their accuracy. Especially the Gamma STT...I can use it five times in five minutes after a racquet is right off the stringing machine, and just about get five different tension results. The Tourna one seems to be a little more accurate, but again, I wouldn't bet the farm on that one either. I've never tried nor used any downloadable app like RacquetTune or whatever it is, so I can't speak on their accuracy or lack thereof.