Slide rule
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A slide rule is a hand-operated mechanical calculator consisting of slidable rulers for evaluating mathematical operations such as multiplication, division, exponents, roots, logarithms, and trigonometry. It is one of the simplest analog computers.
Typical ten-inch (25 cm) student slide rule (Pickett N902-T simplex trig)
Cursor on a slide rule
This slide rule is positioned to yield several values: From C scale to D scale (multiply by 2), from D scale to C scale (divide by 2), A and B scales (multiply and divide by 4), A and D scales (squares and square roots).
A 7-foot (2.1 m) teaching slide rule compared to a normal-sized model
Multiplication
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Multiplication is one of the four elementary mathematical operations of arithmetic, with the other ones being addition, subtraction, and division. The result of a multiplication operation is called a product.
4 × 5 = 20. The large rectangle is made up of 20 squares, each 1 unit by 1 unit.
The Educated Monkey—a tin toy dated 1918, used as a multiplication "calculator". For example: set the monkey's feet to 4 and 9, and get the product—36—in its hands.