Abstract: A selectively alterable base numerical system in which a calculator implemented in a few semiconductor chips has a keyboard to enter numeric data and to command functions to be performed on the data by circuitry on the semiconductor chips in a first number base. The results of operations on the data in accordance with a selected function are then available as by way of a display. Circuitry is provided responsive to a keyboard base function input to change the results between number bases, preferably between hexadecimal, octal and decimal. A three chip calculator is provided where a data chip cooperates with two ROM chips and a manual keyboard input unit to permit operation selectively in any of several number bases and to change between bases at any point in a course of operations.