# Can ISO GPS and ASME Torancing Systems Define the Same Functional Requirements?
## 2 From ASME Y14.5 Specifications to the ISO GPS System Drawing
Two position tolerances are indicated and both shall be considered separately. The position tolerance T = 0.15 mm with respect  
Figure 3:1 (**a**) Specification of position tolerance for flange with respect to the datum axis (ASME Y14.5); (**b**) minimum circumscribed cylinder axis shall be within the cylindrical tolerance zone. Figure 3:2 (**a**) Coaxiality tolerance for flange with respect to datum axis A (ISO GPS), equivalent to the specification given in Figure 11a; (**b**) for coaxiality tolerance, TED = 0 mm is obvious. If the offset between the axes in a complex part will be significantly smaller, there is a risk for the position tolerance that a drawing reader will not detect such offset. to the datum system A | B | C defines four cylindrical tolerance zones of diameter 0.15 mm located by theoretically exact dimensions (dimensions given in rectangular frames), within which the tolerance features--axes of the cylinders inscribed individually to each hole--shall be contained. The datum system A | B | C constrains all 6 degrees of freedom, so these four tolerance zones are locked (Figure 13b). The position tolerance T = 0.05 mm with respect to the datum A defines the next set of four cylindrical tolerance zones of diameter 0.05 mm that are perpendicular to the datum A and, due to ASME Y14.5's default simultaneous requirement, their axes are defined as edges of the rectangular prism with the rectangle base 24 mm \(\times\) 18 mm. The pattern of four cylindrical tolerance zones of diameter 0.05 mm may float, i.e., may translate into any direction parallel to the datum A (plane) and rotate around the axis perpendicular to the datum A. The axes of the four holes shall be within the largest tolerance zones and the smaller tolerance zones, as is shown in Figure 13b. In the ISO GPS system, due to different defaults to specify the same requirement, two modifiers shall be indicated (Figure 14). The modifier CZ, combined zone, shall be used to create the pattern [26] of four cylindrical tolerance zones of diameter 0.05 mm with respect to the datum A and the encircled X shall be used to indicate that the tolerance feature is defined as the derived feature (axis) of the associated maximum inscribed cylinder--the cylinder that is inscribed into the actual surface of each hole. The same plate with four holes is given in Figure 15a, but now the composite feature control frame is specified. According to ASME Y14.5, the composite feature control frame contains a single geometrical characteristic symbol (position or profile), followed by two or more segments, each containing tolerance and any required datum references. The uppermost segment has the largest tolerance value and locates the pattern with respect to the specified datum system. Each lower segment is a feature-relating control that governs the smaller position tolerance within the pattern (feature-to-feature relationship). The datum features specified in the second and all lower segments of a composite feature control frame constrain only rotational degrees of freedom with respect to specified  
Figure 3:3 (**a**) Position tolerance T = 0.15 mm locates the pattern with respect to datum system A | B | C, position tolerance T = 0.05 mm refines the mutual location between holes and limits tilting of the pattern with respect to the datum A (ASME Y14.5); (**b**) tolerance zones—meaning of two level specification. degrees of freedom are not constrained. The datum features in the lower segment shall be specified in the same order of precedence as in the upper segment, and if not listed all, they may be skipped in the order from right to left. In Figure 15a, the position tolerance symbol is \"shared\" twice. The position tolerance T = 0.15 mm with respect to the datum system A 1 B 1 C defines four cylindrical tolerance zones of diameter 0.15 mm located by theoretically exact dimensions, within which the tolerance features--axes of the cylinders inscribed individually to each hole--shall be contained.