# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 2 From ASME Y14.5 Specifications to the ISO GPS System Drawing
The left hole has a complex shape; therefore, it is located by the surface profile tolerance T = 0.6 mm with respect to the datum system A | B | C. The location of the tolerance zone is fixed and the tolerance zone is divided symmetrically into both sides of the theoretically exact profile (marked by the dashed line in Figure 22). The surface profile tolerance applies _all around_ the theoretically exact profile, which is indicated by the small circle placed on the intersection on the leader line and the reference line. The extracted quarter-cylindrical hole surface shall be contained between two boundary surfaces 0.6 mm apart. It means that the quarter-hole form deviations are limited to 0.6 mm. The designer accepted 0.6 mm variability for the quarter-hole in the delivered lots, but in the particular plate, the left hole form deviation is limited to 0.1 mm by the indicated dynamic surface profile tolerance. Regardless of the size of the left hole, its form has to be confined in its separate tolerance zone. This gives a tighter control of the form without tightening the size tolerance given to the feature. The dynamic surface profile tolerance zone is functionally equivalent to the cylindricity tolerance zone applied to the right hole. The datum references may also be used with the dynamic profile to control form, orientation and location without size. The equivalent limits for the left hole specified with the ISO GPS system indications are shown in Figure 2:1 The modifier OZ (_unspecified linear tolerance zone offset_) was introduced in the latest edition of ISO 1101 [12] and its application is explained in ISO 1660 [28]. The modifier OZ indicates that the surface profile tolerance zone is allowed to be offset from being symmetrical around the theoretically exact feature by a constant but unspecified amount. The width of the tolerance zone, T = 0.1 mm, is given in front of the OZ. The modifier UF (_united feature_) is specified in the upper adjacent area to make it explicit that the specification applies to the compound integral feature considered as a single feature. Figure 2:2 (**a**) The ISO GPS system specification equivalent to the requirement given in Figure 19a; (**b**) establishment of the tolerance zone according to the ISO GPS system, new offset theoretically exact feature is marked by the dashed line. Figure 2:3 The dynamic surface profile tolerance for the left hole with a complex shape controls its form in similar way as cylindricity tolerance controls the form for the right cylindrical hole (ASME Y14.5). Figure 2:4 Surface profile tolerance zone (T = 0.6 mm) fixed with respect to datum system A \(|\) B \(|\) C. (**a**) One of the numerous dynamic tolerance zones (T = 0.1 mm); (**b**) another of the numerous dynamic tolerance zones (T = 0.1 mm). The dynamic surface profile tolerance zones are free to translate, rotate and uniformly expand or contract. It should be noted that the surface profile tolerance in ASME Y14.5 is the only tolerance that may be applied to locate a nominally flat surface. In the ISO GPS system, both the surface profile tolerance and the position tolerance may be applied to locate the nominally flat surface and have the same meaning. However, to get better readability of the drawings, it is recommended to apply the position tolerance to locate nominally flat surfaces. The position tolerance in the ISO GPS system carries clear information that the tolerance feature is a nominally flat surface. When the profile tolerance is specified in the ISO GPS system, it is necessary to verify in the drawing or in the CAD model that there is no indication that the feature is nominally non-flat. In ASME Y14.5, specification of the position tolerance is restricted to the derived features of the features of size. It is worth mentioning that both systems recommend using the profile tolerances as general geometrical specifications and general size specifications to ensure univocal specifications for functionally less important geometrical features of a part [13; 29].