Early computers were mechanical machines built using gears and levers. These parts or components could be moved with precision and were connected to other components in a way that simulated the relationship between different variables in a mathematical equation. By moving a gear or pulling a lever, one can change these variables and the results of these actions can be viewed in another set of gears, whose newly acquired positions gave the answer the operator was seeking.
In 1936, a Russian engineer named Vladimir Lukyanov built such a mechanical computer that used not gears and levers but water to compute.
Vladimir Lukyanov’s water integrator. Image credit: www.kramola.info