I used it yesterday on my freshly strung babolat PSLs. I strung them with full 17g synth gut(gamma challenger & Wilson stamina). Out of curiosity I decided to string 1@49lbs and 2nd@48lbs.
Racquettune gave me tension of 48.7lbs and 47.8lbs, respectively(taking multiple readings). I was very surprised at the accuracy. By the way I use a klippermate.