Abstract: A calculator, which may be used for educational purposes, for instance, is preferably provided with an integrated circuit, a display for displaying a number outputted by the integrated circuit, an array of key switches for inputting numeric and functional data to the integrated circuit, a keyset comprising an array of key switch push buttons moveably disposed in openings in a member retaining the array and a case in which the integrated circuit, display and the array of key switches are disposed. The case also is provided with an opening for removeably receiving the keyset, the keyset being disposed adjacent to the array of key switches when received in the opening. The calculator is preferably provided with a plurality of such keysets, the keysets each having different configurations of key push buttons for permitting an operator of the calculator to be able to access either to selected key switches or all key switches depending upon the particular keyset used.