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An iron sight is a system of aligned markers used to assist the eye in making alignments or directional observations when one is aiming a firearm or crossbow. Unlike scopes, iron sights do not make use of lenses. They are instead typically composed of two component sights: the front sight, which is a post, bead, or ring, and the rear sight, which is either open (a notch) or closed (an aperture). On many firearms, the rear sight is adjustable to account for what factors? Discuss
Source: The Free Dictionary