Astolabe, a special computer for star positions

Boulton & Watt engine 1788: the governor is on the right

Analogue computers are mechanical or electronic devices which solve problems. some are used to control machines. They were once the only way a machine could be controlled, and are still used in cases where digital computers are not the best choice. The abacus, a digital device also sometimes called a computer, was used by Babylonians in c. 2500 BC.