The abacus is almost certainly the oldest calculating machine. Historians and archaeologists have traced it back to ancient Roman and ancient Greek times, but it's almost certainly much older than that.
In class I demonstrated a child's toy version, in part because it's easier for me to use; in part because it's larger.
The abacus is the first device, as opposed to a mere system (such as notches in sticks or bones).
An abacus is a very effective calculating tool. The device below was sold in Japan in the 1980s, because people good with the abacus can add and subtract faster with an abacus than with a calculator. However, unless you're very good, multiplication is faster with a calculator, and I think that division and other arithmetic operations are faster with a calculator for anyone.
