| Rebound |
 | | Ball rebound testing equipment |
The rule specifying how the ball should bounce was set in 1925 and is still in use today. The test involves dropping a ball vertically from a height of 254 cm (100 inches) and measuring the rebound, which should (for all Type 2 balls) be 135-147 cm (53-58 inches). The range for balls for use at high altitude is 122-135 cm (48-53 inches).
The equipment used in the ITF laboratory consists of a vacuum pipe that holds the ball at the correct height before being released, a smooth, granite block onto which the ball bounces, and a video camera and light source. Each rebound is recorded and the rebound height measured from the shadow of the ball that is cast against a scale. This is all done with software that analyses the video of the bounce in real time and calculates the height using the contrast between dark (the ball) and light (the background) over a series of frames either side of the peak.
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