What does perpendicularity tolerance control in GD&T?

Perpendicularity is an orientation tolerance that controls how perpendicular a surface, axis, or median plane is to a datum reference. For a surface, the tolerance zone consists of two parallel planes perpendicular to the datum within which the surface must lie. For an axis, it creates a cylindrical tolerance zone. Perpendicularity is commonly used to ensure proper mating of components at 90-degree angles.