A ruler, also called a middle ruler, has a precise straight edge and is used for measuring length and drawing. Widely used in mathematics, measurement, engineering and other disciplines.

Rulers are widely used in mathematics, measurement, engineering and other disciplines. A ruler with a precise ruler. Rulers are used to measure straightness and flatness by light gap method, and can also be used to check length and size together with measuring blocks.

Ruler, also known as interval ruler, is a very common tool for measuring length. This kind of stationery is very common, almost every primary school student has one, which is usually used to measure short distances or draw straight lines.