Reticle

A reticle or reticule, also known as a graticule, is a pattern of fine lines or markings built into the optical path of an optical device to provide measurement references during visual inspections. Reticles are usually built into the eyepiece of spotting scopes, theodolites or optical microscopes, allowing different reticles to be interchanged when changing the eyepiece, although reticles in telescopic sights or the screen of an oscilloscope are permanently fixed in place. Today, engraved lines or embedded fibers may be replaced by a digital image superimposed on a screen or eyepiece. Both the terms "reticle" and "graticule" may be used to describe any set of patterns used for aiding visual measurements and calibrations, but in modern usage reticle is most commonly used for weapon sights, while graticule is more widely used for non-weapon measuring instruments such as oscilloscope display, astronomic telescopes, microscopes and slides, surveying instruments and other similar devices.

There are many variations of reticle pattern; this article concerns itself mainly with the most rudimentary reticle: the crosshairs, which is typically represented as a pair of perpendicularly intersecting lines in the shape of a cross, "+", though many variations of additional features exist including dots, posts, concentric circles/inverted horseshoes, chevrons, graduated markings, or a combination of the above. Most commonly associated with telescopic sights for aiming firearms, crosshairs are also common in optical instruments used for astronomy and surveying, and are also popular in graphical user interfaces as a precision pointer. The reticle is said to have been invented by Robert Hooke, and dates to the 17th century. Another candidate as inventor is the amateur astronomer William Gascoigne, who predated Hooke.

Etymology

The term reticle comes from the Latin word reticulum, meaning "small net". The word graticule comes from the French word graticule, which was in turn derived from the Medieval Latin grātīcula, meaning "small grating" or "small gridiron", and a diminutive form of crātis, meaning "hurdle" or "wickerwork".