We tend to think of calculators as devices house in dull plastic boxes, but these calculators show them for the range of mechanical wonders that they are, from gleaming dials to monkey-shaped viewers to pens from some retrofuturistic world.
The Pascaline or Pascal's Calculator, by Blaise Pascal. It could add, subtract, multiply and divide two numbers (1642)
(via David Monniaux)
The Adall Calculator, a 7.7 in (195 mm) diameter hundred-tooth disc, manufactured in Birmingham, England during the 1910s and 1920s
Consul, the Educated Monkey, originally produced in the early 1920s in Dayton, Ohio. It is a remake from the German DBS, produced around 2005.
The Water Integrator, that could solve (partial) differential equations, built by Vladimir Lukyanov, 1936
The water levels in the chambers represented stored numbers, and the rate of flow between them represented the mathematical operations.
The hand-cranked calculator Curta, invented by Curt Herzstark in 1948. Type II was introduced in 1954 and produced until 1972.
(via Werner Kratz)