An analogue computer – a physical device simulating the target prosess (the phenomenon of interest) using electronic, mechanical or other physical phenomena described by the same mathematical model, but cheaper and simpler to implement.
Historically appears before the electronic digital computer. Mechanical versions are known since antiquity
Kircchoff electrical chains modelling the flow in tubes and underground reservoirs (e.g., applied to petroleum research and other physiacl phenomena governed by systems of differential equations)
