Ruler

A ruler is an instrument used to make length measurements, whereby a length is read from a series of markings called "rules" along an edge of the device. Alternatively, it is called a rule, scale, line gauge, or metre/meter stick. Usually, the instrument is rigid and the edge itself is a straightedge ("ruled straightedge"), which additionally allows one to draw straighter lines. Rulers are an important tool in geometry, geography and mathematics. They have been used since at least 2650 BC. Rulers have long been made from different materials and in multiple sizes. Historically, they were mainly wood but plastics have also been used. They can be created with length markings instead of being scribed. Metal is also used for more durable rulers for use in the workshop; sometimes a raised metal edge is embedded into a wooden desk ruler to preserve the edge when used for straight-line cutting and to prevent ink from feathering under the ruler when used to draw a straight line with a pen. Typically 12 in (30 cm) in length, though some can go up to 100 cm (39 in), it is useful for a ruler to be on a desk or workstation to help in drawing.