Abstract: A pocket calculator includes a main frame which consists of a keyboard, a display and display drivers mounted on a printed circuit board, a case, and a connector for receiving one of a plurality of arithmetic or processor modules. Each processor module includes an arithmetic chip mounted in a package which is, in turn, mounted on a printed circuit board having an edge connector. The case of the calculator has an aperture for receiving each one of the modules. The connector on the printed circuit board of the main frame is mounted in registry with the aperture and is disposed for receiving the module, such that any one of the number of processor modules may be employed with the same calculator main frame.