The earliest form of computing machine, as revealed by history, was not digital but analog. In analog representation, properties of the representational medium corresponds to the represented state-of-affairs.
There are various forms of analog representation, like longer the road, longer the line on a motorway map or greater the number of windows in a building, greater the number of plastic squares in the models. This analog computation originated in 1876, when James Thomson invented the mechanical wheel-and-disc integrator.
This device was constructed for computing the integral of the products of 2 given functions. During World War I, these mechanical analog devices were hugely used for gunnery calculations and Hannibal Ford later improved these devices during the post war period.
The first large scale, automatic general-purpose analog computer built by Vannevar Bush of MIT in 1931, was based on the same wheel-and-disk concept and it was soon accepted worldwide. Subsequently, Bush and his associates replaced the old mechanism by electromechanical and finally by electronic devices.