# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 2 From ASME Y14.5 Specifications to the ISO GPS System Drawing
Due to the maximum material requirement specified for the datum B, the sidewalls of the plate shall not violate the maximum material virtual condition MMVC boundary established by two parallel planes, a distance 50.1 mm apart, perpendicular to the datum A. The MMVC is represented in the gauge by its flank walls. Finally, at least one point of contact is required for the datum feature indicated by letter C with the gauge groove closing side that establishes the datum C. The maximum material requirement specified for the datum B produces additional mobility for the plate with a width smaller than 50.1 mm when it is inserted into the gauge grove. It means, taking into account ASME Y14.5's default simultaneous requirement, that all five holes may be shifted in the same direction and thanks to the smaller plate width it may be possible to move (translate/rotate) the plate to insert the plate holes into the gauge pins. In the ISO GPS system, according to the independency principle, by default, a geometrical specification that applies to more than one single feature applies to those features independently. So, the tolerance zones defined by one tolerance indicator or by several  
Figure 3:7 (**a**) Two position tolerances shall be verified simultaneously (ASME Y14.5); (**b**) the material gauge. tolerance indicators shall be considered independently. Looking at the plate shown in Figure 17a, it is, functionally, very likely that four 8 mm diameter holes shall be located together. To indicate this in the ISO GPS system, modifier CZ (combined zone) shall be specified after position tolerance T = 0.2 mm in the tolerance indicator (Figure 18). The 10 mm hole is another geometrical feature with another position tolerance, T = 0.3 mm. To link together these two position tolerances in one requirement, the modifier SIM (_simultaneous requirement_) is indicated on the right side of each position tolerance indicator (Figure 18). In cases where, the modifier SIM will be not specified the position tolerances for the pattern of 8 mm diameter holes and position tolerance for the single 10 mm hole shall be verified separately. For the two material gauges, close-end slots are necessary. The first gauge has four pins with diameters equal to the maximum material virtual size, MMVS = 7.7 mm. The second gauge has one pin of diameter MMVS = 9.6 mm. It means that when the plate width is smaller than 50.1 mm, then the 8 mm hole pattern and the 10 mm hole may be shifted away in opposite directions. The encircled M--MMR (maximum material requirement [27]) specified after the secondary datum introduces mobility with respect to boundaries defined by the MMC condition. In the case where the datum B will be specified without MMR, the datum system A | B | C is constraining all degrees of freedom and the modifier SIM is not necessary. The surface profile tolerance is used to define a tolerance zone to control the combination of size, form, orientation and location of a feature (Figure 19a), or features, with reference to theoretically exact profile(-s). The surface profile tolerance zones may or may not be indicated with respect to the datum or datum system. By default, in the ASME Y14.5 and in the ISO GPS system, for the surface profile tolerance the tolerance zone is bilaterally (equally) disposed on both sides of the theoretically exact feature (profile) by equal offsets. In some instances, an unequally disposed tolerance zone is required. For example, the disc shown in Figure 19a shall slide precisely along the groove in a cube. It will be quite convenient for such a function to specify the same theoretically exact dimension for both parts and displace, respectively, tolerance zones in both features to eliminate the overlap that will occur in the case of equally disposed tolerance zones. The encircled U  
Figure 3:8 The ISO GPS system specification equivalent to the requirement given in Figure 17a. placed after tolerance T = 0.2 mm (Figure 19a) indicates that the tolerance zone is unequally disposed.