Flatness

A surface is described as planar when all its points lie on a single plane. This means that there is no elevation or depression that would cause points of the surface to lie above or below the imaginary plane.

The technical term flatness refers to this concept of planarity and extends it by specifying a form tolerance. The form tolerance indicates the extent to which the surface may deviate from ideal flatness in order to still be considered functionally flat. These tolerance limits are specified in technical drawings and specifications and serve to ensure that the surface remains within certain limits that are acceptable for the intended use.