Wondering whether or not to restring your racquet? Some people wait until their strings break. Me not being a string breaker I tend to restring if my game feels like it's going downhill. There is a more exact science available.
Take a look at this little gadget called the Stringmeter; Unique Sports sent me one to try. In less than a minute per racquet (I've got three of the same), Stringmeter revealed that two of them needed restringing. One I already knew about because of sliding strings. Only the one that had been recently strung was pretty close to what I had set it at.
Why the tension differences?
Stringing machines do not always generate a like product. A machine set to string at 58 lbs may result in a deviation of four pounds in either direction. Hit with the racquet for a couple of weeks, check again and you are sure to see even more tension loss. You've seen Roger Federer switch racquets between games. This may be part of the reason. Hard hitting effects tension too.
Additionally, if you use different stringing shops know that stretch, racquet distortion, friction, tension, and stringer technique may all factor into dissimilar tensions on the same racquet using the exact same string. The racquet you had strung at 60 lbs in Florida may not be exactly like the one you had done locally.
At 2.5 or 3.0 this may all be a mute point but the much higher level player can definitely feel the difference when tension is off.
The Stringmeter retails for $34.99 USD and measures string diameter and tension in pounds and kilograms during stringing and after. The techie in me thought it was useful and kinda' fun. Buy at Tennis-Warehouse and UniqueSports.