A pocket calculator comprises two registers, named X and Y$,$ each of which are composed of $84-$bit registers. The X$-$register is also responsible of maintaining the the display information, while the Y$-$register acts as an accumulator to perform the transfer operation Y $$ X $+$ Y$.$The controller feeds numeric data into the X$-$register serially. Each time the $+$ key is pressed, X $+$ Y is transferred to both registers. The display will continue getting numeric data upon displaying the summation result. Both registers are cleaned when $$C$$ is entered by the user.