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Calibration question

Q: In doing some research about how to calibrate my lock-out machine, I have found that some people do it with the calibrator going directly from the clamps to the string gripper, while others mount a racquet and simulate a string pull that might occur while stringing a racquet. Which one is a better practice?

A: The standard procedure is to calibrate without having a racquet mounted. This eliminates other factors, so that you can set the tension head to pull at the reference tension. Attempting to calibrate with a frame mounted (and the leads to the calibrator running through grommet holes) introduces friction into your calibration attempt and increases cosine error — which is caused due to the typically linear pull of the machine working at an angle to the actual direction of the pull on the string.

It is easy to understand why someone would want to try to mock up a racquet in progress for the calibration procedure, but the frame-in technique introduces more problems than it eliminates. If it is really that important to have the reference tension accurately transmitted to the string as it runs through the racquet, the best approach is to buy a machine such as the Babolat Sensor Expert, which has a tension head that rises to the level of the stringbed during tensioning.

From the May 2007 issue
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