It has 3 7-segment displays with a display if a number is negative (-), a binary to BCD (double dabble), BCD to binary, decimial to binary, CCA adder/subtractor (2s compliment to sign and magnitude), combinational multiplier, 2 buttons to clear numbers, 2 buttons to add selected digit, 2 buttons from 0-9, 3 buttons to select operation (- and * ; it is addition by default), and a calculate button
Firstly unselect all levers 0-9. Press clear number. Select number from 0-9. Press add digit. Unselet number. If it a 2 digit number, select another one and press add digit. Do the same for the other input. Select operation (addition is by default). Press calculate.