Issue link: http://itf.uberflip.com/i/450983
13 Figure 4. Rebound – Test Method ITF TB 04/01. To ensure sufficient accuracy of the rebound measurement, the following method is recommended. A shadow of the ball produced by a parallel and horizontal beam of light is cast onto a vertical frosted screen incorporating a graduated calibrated scale. Images of the shadow are captured by a video camera, and the trajectory of the ball analysed such that its highest point with reference to the calibrated scale can be identified. Durability – Test Method ITF TB 05/01: The ball is projected such that it impacts a smooth, rigid surface mounted at 90 ± 10° to its trajectory at 40 ± 3 m/s with 3 rev/s spin. This procedure shall be repeated until the ball has undergone 20 impacts. The ball shall then be placed in a felt-wearing device, with a second ball, for a period of 2 minutes. This wearing procedure (the "wearing regime") may be performed outside of the Controlled Environment. Following this procedure, the ball is conditioned in the Controlled Environment for a minimum of 24 hours and then retested for rebound, size, mass and deformation in accordance with the procedures described herein. In all tests for durability, the felt-wearing device shall consist of a box lined with medium grade emery paper (which shall be obtained from the ITF), and inclined at 23° to the horizontal, with three rotating wooden spigots at the lowest point. The internal dimensions of the box shall measure 15 ± 1 cm by 15 ± 1 cm and 69 ± 1 cm in length. Each spigot shall measure 19 ± 1 cm in length and 2.0 cm in diameter, and shall be rounded at both ends with a radius of 1.0 cm. The angle between the spigots, measured about the centreline of the axle, shall be 60°. The distance between the centrelines of adjacent spigots shall measure 4.5 cm. Each spigot shall protrude 4.0 cm into the box, when parallel to the bottom end face of the box, and the centreline of the spigot shall measure 3.0 cm to the aforementioned face when in this position. The angular velocity of the spigots shall be 500 ± 50 rpm. See Figure 5.