backsights

Backsights are sighting references located at the rear of a device used for aiming or measurement. The term is used in firearms, archery, and surveying to describe a reference point that, when aligned with a front sight or a known target, helps determine the line of sight or height difference. In both contexts, the backsight serves as a reference that supports accurate alignment.

In firearms and archery, the backsight is paired with a front sight to form a complete sight picture. With iron sights, the shooter aligns the rear notch or aperture with the front sight post and the target. In specialized systems, the rear sight may be adjustable for windage and elevation, or it may be a fixed peep or diopter used together with a front sight. The accuracy of aiming depends on proper alignment and calibration of both sights.

In surveying and leveling, a backsight refers to the observation taken from the instrument toward a known rod or staff. It is used to determine the height of the instrument (HI) and to calculate elevations by comparing it with foresight readings taken at points of unknown elevation. The backsight establishes a reference height that enables subsequent measurements to yield relative elevation changes.

The term contrasts with foresight in surveying and with the rear sight in aiming systems. Across uses, backsights require careful alignment and consistent reference points to maintain accuracy.