Measurement Accuracy

Several things can affect measurement accuracy. Generally, these become important when trying to achieve better than ±1 kg•cm² accuracy.

Device Leveling

The device rotation axis must be vertical for accurate measurement. Deviations from vertical will allow gravity to influence the pendulum motion. To see the effect, first measure a racquet with the device properly leveled. Then, turn the rear leveling foot a full turn in either direction and measure the racquet again.

Racquet Release

For the most accurate measurement, hold the cradle of the SW1 against the stop lightly prior to release. If held with too much force, some elastic energy may be released that will affect the measurement.

Temperature

The spring that drives the SW1 is wound of spring steel. Like most materials, it becomes less stiff as its temperature rises. For the most accurate measurement, the ambient temperature during measurement should be nearly the same as it was during calibration. For a typical tennis racquet, the measured swingweight increases by approximately 0.09 kg·cm² per °F (0.16 kg·cm² per °C) of temperature rise.

Additionally, accuracy of the first measurement after sitting idle can be improved by performing a mock measurement to “warm up” the spring prior to measuring.

Alloys with elastic properties that remain stable across temperature changes have been developed for use in timepieces. Unfortunately, such a spring for this application would be quite expensive.

Air Currents

Air currents can affect measurement, so avoid placing the SW1 near a fan or vent. To see the effect, measure a racquet in still air and again while blowing on it. In the measurement group display, note the difference in Fit Residual values between the two measurement. A greater residual indicates that the data fit is less optimal.

Surface Stability

The SW1 should be placed on a stable surface. Any movement of the surface will reduce accuracy.