The term 'Adding Device of Old' can be summarized as an ABACUS, which is a 6-letter word. An ABACUS is an ancient calculating tool that was used in many parts of the world for centuries. It consists of a frame with beads or other counters that are moved along rods to perform calculations. The ABACUS is still used in some parts of the world today, although it has been largely replaced by modern calculators and computers.