Abstract: A calculator adapted to be used with a push button telephone having an array of telephone push buttons for serving both as a calculator and as an enlarger for the push buttons to facilitate the actuation of them, includes a first array of finger discs corresponding to at least some of the telephone push buttons and extending from a cup-shaped housing having an open mouth adapted to fit over the array of telephone push buttons, the first array of finger discs enabling the user to actuate the telephone push buttons. Logic circuits are mounted within the housing for performing mathematical calculations, and a display device mounted on the housing responds to the logic circuits for indicating information concerning the calculations. A first set of switches are mounted on the housing and respond to the finger discs for causing the generation of input information for the logic circuits.