Chapter 9 Profile Tolerances 335 Specifying Basic Dimensions in a Note A general note can be used to specify basic dimensions. Use the general note “UNTOLERANCED DIMENSIONS ARE BASIC” rather than using the customary rectangular block around the dimension to denote basic. Refer to Example 9-11. This general note was once used to save time in manual drafting in situations requiring an extensive number of basic dimensions on the drawing. This issue is not a problem when using CADD, because basic dimensions are placed quickly. It is better to use the basic dimension symbol on basic dimensions for clarity. There is a good reason not to use the general note. When the note is used, the reader of the drawing must understand GD&T and know when basic dimensions are used and their specific applications. The reader must also sort through the dimensions to determine which dimensions are basic and which are plus/minus. This can be difficult for the reader and some dimensions can be missed if dimensions that rely on the tolerances in the title block are used. The general note should be avoided to reduce misinterpretation of the meaning of the drawing. Check with your company or instructor before using this method to determine if it is appropriate. Combination of Geometric Tolerances Profile tolerancing can be combined with other types of tolerancing. For example, a surface can have a profile tolerance controlled within a specified amount of parallelism relative to a datum. When this is done, the surface must be within the profile tolerance, and each line element of the surface must be parallel to the given datum by the specified parallelism tolerance, as shown in Example 9-21. 0.15 sectional tolerance zone parallel to datum 0.5 profile tolerance zone Datum plane X Datum plane Y The Drawing The Meaning Example 9-21. An application of geometric tolerances combining profi le of a surface between two points and single element parallelism.