This iPhone app claims to be able to tell your string tension based on the sound of your racquet. http://appmaker.se/racquetTune.html http://www.racquetsportsindustry.com/news/2010/04/test_your_racquets_with_an_iph.html A question to the experienced stringers on this board - would this work - or even be semi-accurate??? It does have an option to set the your head size, linear density, string type, string thickness, but I would think that based on the various materials used in racquets now days and the various composition of strings, it would be hard to estimate tension based on the sound/frequency of the strings. Does anyone have/use a similar tool???