The speed measurement is usually working with normal balls. For best accuracy and spin measurement, we require SPINSIGHT balls but when the app cannot find our dots, it will still display the speed result.
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You can see the live result for the speed in the Playground and use the speed based trainings "Serves - Fast Long" and "Attack - Smash".

Occasionally the app may be confused by the stamp or other patterns on the ball and it may show a spin value with normal balls. These sporadic spin results are not reliable and should not be used for training.