an improved wristwatch calculator has all of the active circuit elements contained on three chips mounted on the same substrate member in the watch case . a watch chip and a calculator chip each have their outputs connected to a single interface chip consisting of cmos or i 2 l active elements which multiplex the watch and calculator chip outputs and select the appropriate display as a function of watch mode selection by pushbutton or inertia time demand switches or calculator mode selection by activation of the appropriate calculator keyboard switch on the watch face . the interface chip outputs are connected to six electro - optical display stations .