# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 2 From ASME Y14.5 Specifications to the ISO GPS System Drawing
Specifications in Figure 4a,b seem to be identical, but the default interpretation of the local size is different  
Figure 3: (**a**) Two coaxial holes shall be considered as one feature of size (ASME Y14.5); (**b**) common tolerance with the envelope requirement is applied to two separate single features of size to consider them as one feature of size (ISO GPS). To accept a part in both tolerancing systems, one cylinder with a diameter not less than 18 mm shall be inscribed into two holes simultaneously. Figure 2: (**a**) Shaft with limit sizes specified according to the ISO GPS system indications with requirements equivalent to those given in Figure 1a (ASME Y14.5); (**b**) the envelope requirement (ISO GPS) is not fully in line with requirements given in Figure 1a. in ASME Y14.5 and in the ISO GPS system. The equivalent specifications are shown in Figure 5.  
The circularity (roundness) tolerance specified in Figure 6a is listed in ASME Y14.5 as the form tolerance, and in ANSI B89.3.1 [25], further information is given. ANSI/ ASME B89.3.1 states, by default (i.e., without any additional symbols), that for roundness measurement, the following conditions apply: reference method, MRS (minimum radial separation); filter, 50 UPR (undulation per revolution); and tip radius, 0.25 mm. Currently, default measuring conditions for roundness tolerance are not specified in the ISO GPS system standards, but ISO 1101 [12] provides symbols that a designer may use to set up measuring conditions (Figure 6b). The specification element CB indicates that a closing ball filter is specified. The value \"0.25\" indicates that a 0.25 mm radius ball shall be used as the structuring element and, because it is followed by \"-\", it is a long-wave pass filter, which removes short wavelengths. The closing ball filter may be physically implemented as the diameter of the ball stylus tip. The specification element G indicates that a Gaussian filter is specified with nesting index 50 UPR. Due to the fact that the value \"50\" is followed by \"-\", it is a long-wave pass filter, which removes short wavelengths (higher UPR values). The specification, therefore, applies to a feature (circumferential line) that has been digitally filtered with a 50 UPR Gaussian long-wave pass filter. By default, each individual filtered circumferential line shall be contained in a tolerance zone defined as the space between two concentric circles with the 0.03 mm radius difference. It is worth mentioning that in American Standards, default conditions are only specified for roundness deviation measurement. The default conditions for measurement of other form deviations (cylindricity, flatness and straightness) are not given. Figure 4: (**a**) Shaft with straightness tolerance for derived median line and size tolerance (ASME Y14.5); (**b**) shaft with straightness tolerance for derived median line and size tolerance (ISO GPS). Local sizes are defined differently. Figure 5: In the ISO GPS system, the straightness tolerance for derived median line and the size tolerance with modifier local size defined by a sphere (letters LS placed in in the elongated circle) defines identical requirements as the specifications given in Figure 4a. According to ASME Y14.5, when profile tolerance is applied to a few features without datums, the tolerance features are by default regarded as the interrupted feature (pattern of coplanar surfaces) and the tolerances are applied simultaneously. In Figure 7a the profile tolerance controls flatness and coplanarity of two nominally planar surfaces (Figure 7b). In the ISO GPS system, according to the independency principle [23], by default, each profile tolerance will be applied separately, the first one to the left top surface and the second one to the right top surface, thereby individually controlling the flatness of each surface. To make the specification easy to understand, it is better to indicate the flatness tolerance symbol instead of the surface profile.