A reticle is a set of two or more crossed or parallel wires that are placed superimposed in the field of view of a scope or other optical device to specify the view or to carry out stadimetric or telemetry measurements.

It is an essential part of a theodolite, a topographic level or a tachymeter, although it is also carried by other optical devices such as: the telescopic sight of a rifle, certain types of magnifying glass or microscope, etc.

Abbot Picard was the first to use a telescopic sight equipped with a reticle.

The Cross hair is a reticle that improves the precision of an optical device, inserting into the field of view, a single (or double) cross of threads that serve as a reference to center the alignment or to measure something.

They are normally located inside a monocular or another type of device (e.g., a magnifying glass, a microscope, binoculars, etc.).

A light flush with the threads allows them to be seen illuminated in the field of vision.

Since these threads must be very thin (to improve accuracy), and the optics where they are mounted tend to magnify them, spider thread has long been used to make them; Today they are already synthetic.

The small viewfinder "Viewfinder (photography)") that accompanies a refracting telescope in its movement in search of stars, known as finder, includes a Cross hair reticle to improve the precision in centering the astro object.

• - Parallax.

• - Alidada.

• - Binocular.

• - Theodolite.

• - Stadimetric rangefinder.

• - Look (topography) "Look (topography)").

• - Glasses.

• - Clinometer.

• - Groma (measuring instrument) "Groma (measuring instrument)").

• - Graphometer.

• - Tachymeter.