The form and location tolerance of a feature (surface, axis, point or median plane) defines the zone within which every point of this feature is to be contained. Depending to the feature to be toleranced and the manner in which it is dimensioned,the tolerance zone is one of the following:

• the area within a circle
• the area between two concentric circles
• the area between two parallel, straight lines
• the area between two equidistant lines
• the space between two parallel planes
• the space between two equidistant surfaces
• the space within a cylinder
• the space between two coaxial cylinders
• the space within a parallelepiped

For location tolerances it is necessary to define a datum indicating the exact location of the tolerance zone. A datum is a theoretically exact, geometrical feature (e.g. an axis, plane, straight line, etc.); datums can be based on one or several, datum features. The toleranced feature may have any form, location or orientation within the tolerance zone, unless a more restrictive specification is given.

The unit of measurement for the tolerance value t is the same as for workpiece dimensions. If not otherwise specified, the tolerance applies to the whole length or surface of the toleranced feature.