The ICs based on their function: The NRD 2256 handles numerical read-in and display, converting keyboard scan-codes into digit values and activating the various display tube segments based on digit values. The DC 2266 does decimal-point control, performing the automatic floating-decimal logic and aligning decimal points for arithmetic operations. The AC 2261 controls the arithmetic and provides the registers the AU 2271 performs the arithmetic (using a digital adder) and controls input to the registers