Abstract: A manual calculator useful in registering and converting whole and fractional numbers from one numbering system to another numbering system in which a plurality of slide members are arranged in an array within a cover, with each said slide member being movable relative to the cover between first and second positions. The slide members each bear indicia indicative of the selected ones of two states, and the cover defines an elongate window in which the indicia borne by the slide members are visible in an array indicative of a selected number series in a first numbering system.

Abstract: The present tennis scoring system includes input devices for each player to indicate whether one player or the other has won a particular point. These input devices for each player may be in the form of transmitters each having two recessed pushbutton switches, one to indicate that one player has won the point and the other to indicate that the opposing player has won the particular point.The input device may take the form of a belt buckle size unit worn at the waist or on the wrist. Electronic scoring circuitry is provided which is responsive to the concurrent depressing of buttons by both players indicating who has won a particular point. Electronic scoring equipment keeps track of the points, games, sets and matches won by each player and each side. Suitable electronic equipment is provided to accommodate slight differences in the timing of the pressing of input switches by the two players. Special logic circuitry is provided for accommodating the tennis scoring situation involving deuce games.