# 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 0 mm following the encircled U indicates the value of the tolerance in the direction that would allow additional material to be added to the theoretically exact profile. So, in Figure 19, the maximum material boundary coincides with the theoretically exact profile. All points of the extracted profile shall be contained in the tolerance zone shown in Figure 19b, which starts from the theoretically exact feature and extends into the material. A quite different notation to specify the unequally disposed tolerance zone is implemented in the ISO GPS system (Figure 20a). The value 0.1 mm indicated after modifier UZ (_specified tolerance zone offset_) sets the diameter of the spheres defining the new shifted theoretically exact feature. This new offset theoretically exact feature is defined as a surface that envelops auxiliary spheres of diameter 0.1 mm (Figure 20b) that are rolled on a primary theoretically exact feature defined by the theoretically exact dimension with respect to the datum A. The datum A, the axis established by the cylinder inscribed in the hole, defines the origin of the theoretically exact radius of 30 mm. The sign plus or minus given between the modifier UZ and the auxiliary sphere diameter determines whether the spheres shall be rolled outside (the positive value) or inside (the negative value) of the theoretically exact feature material. The offset tolerance zone (Figure 20b) is limited by two surfaces enveloping spheres with diameters of 0.2 mm, the centres of which are situated on the theoretically exact surface that was generated by the auxiliary spheres of diameter 0.1 mm. For many years, as was mentioned above, the profile tolerance was used to control a combination of size, form, orientation and location respectively to the datum indication. It is due to ASME Y14.5's default that the profile tolerance zone follows the theoretically exact profile of the considered feature. There was no possibility to control only the form of a toleranced non-planar feature, even for the profile tolerance without a datum(s) because it shares the same tolerance zone for dimensions and form. In ASME Y14.5-2018, a new modifier, _dynamic profile_, indicated by a triangle placed after the tolerance value in the tolerance indicator (Figure 21) was introduced. The dynamic profile modifier shall be specified when it is necessary to refine the form but not the dimensions of the toleranced feature. The form of the toleranced feature is controlled independently of the dimensions. When the dynamic profile tolerance is applied, the tolerance zone may progress (expand or contract) normally to the theoretically exact profile while maintaining its width. The offset between the boundaries of the dynamic profile tolerance zone remains fixed but the size of the boundaries is variable. The actual feature shall simultaneously be within the dynamic profile tolerance zone and the other specified tolerance zone. Figure 3:9 (**a**) The surface profile tolerance with modifier (ASME Y14.5); (**b**) meaning—0 mm outside the theoretically exact feature implies that the whole tolerance zone is inside the maximum material boundary. The dynamic surface profile concept may be well explained on the plate shown in Figure 2:0 The right cylindrical hole is located by position tolerance T = 0.6 mm with respect to the datum system A | B | C and the hole size (surface variability) is controlled by Rule #1 with the diameter limit deviations \(\pm\)0.1 mm. It means that the hole form deviations due to the size tolerance are limited to 0.2 mm. The designer decided that this is too much and additionally specified the cylindricity tolerance T = 0.1 mm. The extracted cylindrical hole surface shall be contained between two coaxial cylinders with the difference in radii of 0.1 mm.