Excerpt:
500 B.C. The abacus was first used by the Babylonians as an aid to simple arithmetic at sometime around this date. The abacus in the form we are most familiar with was first used in China in around 1300 A.D.
1623 Wilhelm Schickard (1592-1635), of Tuebingen, Wuerttemberg (now in Germany), made a "Calculating Clock". This mechanical machine was capable of adding and subtracting up to 6 digit numbers, and warned of an overflow by ringing a bell. Operations were carried out by wheels, and a complete revolution of the units wheel incremented the tens wheel in much the same way counters on old cassette deck worked.