Abstract: A system is described for the automatic detection of ball bounces on a tennis court, and which is applicable to similar games. The system comprises a sonar-like sound system in conjunction with a pressure-sensitive system located on the court surface itself. The sound system uses a multiplicity of microphones to detect and means to analyze the sounds and to calculate the position of sounds identified as balls striking the court surface. The pressure system is used to detect ball bounces on the boundary lines themselves, and utilizes coaxial cables as the sensing elements. The pressure system is checked only when the sound system determines that a ball is bouncing on or near one of the boundary lines. Processing is done by a personal computer to which a special interface card is added.

Abstract: A multi-digit, mixed-base or mixed-radix counter of the type used in digital computing devices wherein the value of each digit of the counter is stored in two parts: a first part being the normal numerical value except in certain exceptional cases; and a second part which is zero except in the exceptional cases in which it is a binary one. The exceptional case is when the value to be represented by the counter digit is a terminal digit value, i.e., a maximum digit value when the counter is incrementing or zero value when the counter is decrementing. In the case of a decrementing counter where the normal terminal digit value is a zero, each zero value is replaced with the corresponding maximum digit value for that digit in the first part of the counter, but the second part of the counter identifies in which (if any) of the digits of the first part of the counter such a substitution has been made.