Far left is one 4-bit input and just to the right is another 4-bit input {1,2,4,8} it adds the numbers from the two 4-bit adders and displays 0-9,a-f on the 7sd.
The top button is the carry. The fourth bit on each input doesnt work here since there is a carry to another circuit, so only the first three bits can be added together with the carry at the top! Enjoy
