An early computer

The comptometer was originally introduced in the 1880's, and was in use well past the 1970's - a hundred year life.

I found one that was built in 1932 at a garage sale for $1. The keys were jammed. The repair manual is available on-line, and the machine is great fun to work on. The works of the machine is mainly springs and stamped steel levers. There are pitfalls available for the unwary, so a close reading of the repair manual is advisable before starting work.

The operator has all ten fingers on the keys during operation. It will add, subtract, divide etc. The operation manual is also online. These machines appear on EBay frequently and can be quite inexpensive ( except for the early wood case models, which are expensive)

http://en.wikipedia.org/wiki/Comptometer