Issue link: http://itf.uberflip.com/i/450983
43 5. BALL REBOUND (PREDICTIVE METHOD) Although the rebound height of a ball is affected by its incident angle, a vertical drop can provide an indication as to the suitability of a surface for tennis. To minimise the effects of environmental conditions and ball properties, the test surface is measured relative to the rebound height on a reference surface. Apparatus Test apparatus consists of: Standard ball. Reference surface, which shall be smooth, rigid and horizontal, e.g. polished granite block. A means to measure rebound height, calibrated to ± 1%, such as a measuring staff and video camera. Calibration of apparatus Check the height-measuring accuracy of the apparatus against a known standard prior to testing. Test procedure 1. Drop the ball from a known height (at least 127 ± 1 cm) onto the reference surface five times and measure the rebound height (BHT) on each occasion, ensuring that there is no parallax error in the measurement. 2. Repeat step (1) on the test surface. Note: The ball should be dropped in a manner that does not impart any impulse or spin. Calculation of results The Relative Percentage Rebound (RPR) is given by: RPR ref test BHT BHT 100 where: BHT test = rebound height on the test surface BHT ref = rebound height on the reference surface