ITF

40 Calibration of apparatus The reference test devices are those belonging to the ITF, and all other devices are calibrated with respect to them. Calibration of test devices is achieved using standard surfaces every two years. Test procedure 1. Adjust the ball-projecting apparatus to deliver the ball at an incident angle of 16 ± 2° and speed of 30 ± 2 m/s. If possible, avoid using the test location(s) and test balls during this preparation stage. 2. Project each of the three test balls onto the test surface three times (nine impacts in total), moving impact location for each shot. If the surface is disturbed or damaged by the test (e.g. movement of clay particles), restore the surface or use a proximate impact location for the next shot. 3. For any surfaces that have an inherent directional pattern – such as natural or artificial grass – test shots should be fired in the typical directions of play, i.e. parallel to the length of the court. Calculation of results Include the following results in the test report for each impact: ν ix = horizontal inbound velocity (m/s) ν iy = vertical inbound velocity (m/s) ν fx = horizontal outbound velocity (m/s) ν fy = vertical outbound velocity (m/s) e = coefficient of restitution (COR) µ = coefficient of friction (COF) T = mean ball temperature for test location/sample (°C) c = temperature coefficient (0.003) e T = adjusted COR for temperature T a = pace perception constant (150) b = mean coefficient of restitution for all surface types (0.81) CPR = Court Pace Rating where: iy fy ν ν e e ν ν ν µ iy fx ix 1 T e e T 23 c CPR T e µ b a 1 100 The test value is the mean CPR for all impacts, excluding court markings. The variation is given by the maximum difference in the mean CPRs for each location, excluding the court markings.

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