The line ruler is a length measuring and positioning element made of metal or glass, and the surface is accurately engraved with parallel lines of equal spacing, also known as a line ruler. The line spacing of the line ruler is generally 1 mm or 0.1 mm.

Metal line rulers are generally made of iron-nickel alloys, and also made of stainless steel, or nickel-plated or chrome-plated on the steel substrate. Glass line rulers are generally made of optical glass with a coefficient of linear expansion close to that of metals.

Line ruler can be divided into reference line ruler, standard line ruler and working line ruler.

The reference line ruler and the standard line ruler are used for the transmission of the value of the length measurement.

The working line ruler is used as a measuring element in length measuring tools such as length gauges, length measuring machines, universal tool microscopes, and universal measuring machines; it is used as a positioning element in precision machine tools such as coordinate boring machines and coordinate grinders. When positioning, it should be used with reading microscope, optical reading head or photoelectric microscope.

An angle-measuring element with an accurately divided scale on the circumference is called a dial. It is commonly used in optical indexing heads, optical rotary tables, etc., and is generally made of optical glass.