314 GD&T: Application and Interpretation Copyright Goodheart-Willcox Co., Inc. the number of parts that must be inspected. The pre- vious discussions are intended to explain the part requirements created by position tolerances and are not intended to require a specifi c means for inspection. Advantages of Position Tolerances Position tolerances have advantages when compared to the use of directly applied coordi- nate tolerances for defi ning location requirements. One advantage is the clarity of the requirement pro- vided by a position tolerance. When the datums, basic dimensions, and position tolerance are properly applied, there is only one correct interpretation of the requirements. Position tolerances also have the advan- tage of permitting the maximum amount of tolerance that is acceptable in the design. Maximizing the toler- ance zone is accomplished through the application of circular zones for round features and through the use of MMC and LMC to gain additional tolerances. All the freedom and fl exibility needed to meet any design application is available when using posi- tion tolerances. Based on design function, position tolerances may be used to specify the necessary toler- ance, whether small or large. The position tolerance may be applied on any product geometry where the need exists, whether the geometry is simple or com- plex. The specifi ed position tolerances are applicable regardless of fabrication process. They may be used on machined, cast, or molded parts, as well as on sheet metal, composites, and parts made using addi- tive manufacturing processes. Saying it another way, position tolerances are a method of clearly specifying what is required regardless of the magnitude of the allowable tolerance and regardless of the fabrication process. Clarity of Position Tolerances There is a well-defi ned meaning for any prop- erly specifi ed position tolerance. Coordinate toler- ances (plus and minus tolerances) applied on location dimensions are not clear in meaning and are subject to interpretation. The requirements communicated by position tolerances are clearly stated in contrast to the lack of clarity and possible confusion caused by plus and minus tolerances on location dimensions. The clarity of a position tolerance is attributed to several factors. One signifi cant factor is the doc- umented meaning and interpretation provided in the ASME Y14.5-2018 dimensioning and tolerancing standard. Position tolerances are well-defi ned by this standard. Written standard guidelines are important because they eliminate the need for people to assume a set of rules by which to interpret dimensions. Using a dimensioning system that has no standardized interpretation leaves the product defi nition subject to varying interpretations and possible disputes. There is no defi ned meaning of directly applied coordinate location tolerances (plus and minus toler- ances) in the ASME Y14.5-2018 standard. Therefore, the use of coordinate location tolerances leaves the product defi nition subject to varying interpretations, which potentially leaves the design requirements vague or without meaning. The use of position toler- ances on features of size avoids the ambiguity of plus and minus tolerances on location dimensions. Another contributor to the clarity of position tolerances is the fact that tolerance zones are located relative to referenced datums. See Figure 8-23. The datum feature references in the given fi gure cre- ate a datum reference frame made of three mutually perpendicular planes. The datum reference frame provides a clear reference from which to manufac- ture and inspect the part. The datum reference frame created by datum feature references in a position Orthographic views Goodheart-Willcox Publisher Figure 8-23. The position tolerance zones and virtual conditions are located on a tolerance zone framework that includes the true positions for all features and is related to the specifi ed datum reference frame.