Applications for such adjusted standards may be made by any National Association to the International Tennis Federation and if approved shall be adopted for such localities. The ball shall not drop through the smaller opening by its own weight and shall drop through the larger opening by its own weight. In all tests for deformation under Rule 3, the machine designed by Percy Herbert Stevens and patented in Great Britain under Patent No. 230250, together with the subsequent additions and improvements thereto, including the modifications required to take return deformations, shall be employed. Other machines may be specified to give equivalent readings to the Stevens machine and these may be used for testing ball deformation where such machines have been given approval by the International Tennis Federation. All tests to be completed within two hours of pre-compression.
Measurements are to be taken from the concrete base to the bottom of the ball.
The ball is placed in position on the modified Stevens machine so that neither platen of the machine is in contact with the cover seam. The contact weight is applied, the pointer and the mark brought level, and the dials set to zero. The test weight equivalent to 18 lb. After waiting ten seconds the pointer is adjusted to the mark if necessary. This procedure is repeated on each ball across the two diameters at right angles to the initial position and to each other.