Arduino + LCD demonstrating the 4008 IC Full Adder !
The 2 red DIP Switches are the 2x4 bit inputs and the 5 LEDs are 4 bit output + one LED for the Carry out bit!
And here is some information about Adders and full Adders (Wiki):
In electronics, an adder or summer is a digital circuit that performs addition of numbers. In many computers and other kinds of processors, adders are used not only in thearithmetic logic unit(s), but also in other parts of the processor, where they are used to calculate addresses, table indices, and similar.