Location Tolerances: Position, Concentricity, Symmetry, and Bonus Tolerance
Position and the bonus system
Position locates an axis, center plane, or surface using basic dimensions from the datums, with the tolerance stated in the feature control frame. For a hole the default zone is a cylinder whose diameter is the frame value, centered at true position. Position controls location, orientation, and, within the zone, form of the axis; it does not directly control the surface location, which is why the virtual-condition boundary matters.
Bonus tolerance appears whenever MMC follows the tolerance value: allowable geometric error grows one-for-one as the actual mating size departs from MMC. Allowed zone = stated tolerance + (actual mating size minus MMC). LMC works the same way in the opposite direction and is used where minimum clearance or wall thickness must be protected. Zero position at MMC converts all size tolerance into bonus and is a legitimate, often superior, callout.
Concentricity and symmetry were removed from the 2018 standard. They controlled the median points of opposed elements, were nearly impossible to verify, and are replaced by position or profile. If a question displays them, it is testing the older standard.
Worked example: a hole toleranced 8.0 plus or minus 0.1, with position 0.2 at MMC to A, B, C. MMC for an internal feature is the smallest size, 7.9. Virtual condition = 7.9 minus 0.2 = 7.7, the smallest boundary the hole may generate. If the hole is produced at 8.1, bonus is 0.2 and the total zone becomes 0.4.