It is possible. But as you said in some cases it becomes guesstimate when (for example) I am unfamiliar with the tension (as my usual is 31-34lbs so below 22lbs is a little unfamiliar to me). The important thing to pick up on in this case is experience. To some degree, most professional players can also identify if the tension on one of their racquets particularly is at the tension that they want to play at. This happens a lot when you see a player changes racquet and just before deciding on which to use next, they will keep hitting their palm on the string bed and listen to the resonant frequency. If you are already used to playing with a particular tension, you should know if the tension has dropped on the racquet. And of course by guesstimate, since I have racquets done at tensions of 31, 32, 33 and 34lbs, I am tuned to the resonance of each tension and when I detected an in-between sound when the temperature changed, I can only just guess that it is a 0.5lbs change. As I have said, the change is not significant and almost not noticable in usual cases.
Blitzzards, Just switch from your HTC to the iPhone and you'll never have to do anymore "guesstimating".
It is more important than absolute pitch in a musical sense as you can tune quicker with other musicians playing with you. This is also how jazz, bebop and blues improvisations are done. That is why it is called relative to concert pitch.
