History of Computers and Computing, Mechanical calculators, 18th century, Johann Müller
- The German engineer and master builder—Johann Helfrich Müller (1746-1830) (see biography of Johann Müller) is a very interesting figure in the world of mechanic calculators, not only for his small calculator, an improved version of the machine of Philipp Hahn, which he created, but for his plans to build a difference engine almost 40 years before Charles Babbage.
Johann Müller was a creative mind and started to make inventions from the beginning of 1770s. First he created a theatre, equipped with optical and mechanical effects for the children of the Prince, later on he designed a large and powerful burning mirror, as well as other devices.
In the beginning of 1780s Müller was asked by the local superintendent's office to check and recalculate some tables relating to the volumes of trees. To shorten this task he had come up with the idea of a machine for the purpose. Soon he realized however that with a few small changes, he could get the machine to perform subtraction, division and multiplication as well. At this stage, he came across an article about the calculating machine of his compatriot, Philipp Hahn, which de decided to use as a prototype, and to try to improve somehow.