316 Geometric Dimensioning and Tolerancing Profile tolerances are always equally disposed bilateral unless otherwise specified. An equally disposed bilateral tolerance is where the tolerance zone is split equally on each side of true profile. Profile tolerances can be specified as unequally disposed bilateral or as unilateral tolerance zones. An unequally disposed bilateral tolerance is where the tolerance zone is split on each side of true profile, but the distance on each side is not equal. A unilateral tolerance is where the entire tolerance zone is on one side of the true profile. A profile tolerance can also be specified between two given points, all around the object, or all over the entire part. The term disposed refers to the distribution of material added to or removed from the part on the specified side of true profile. A profile tolerance is specified by connecting the feature control frame, using a leader, to the view or section that clearly shows the intended profile. There are two types of profile geometric tolerances: profile of a line and profile of a surface. Profile of a Line The profile of a line tolerance is a two-dimensional or cross-sectional geometric tolerance that extends along the length of the feature. The profile of a line symbol and associated feature control frame are shown in Example 9-1. The datum reference is provided in the feature control frame because the profile geometric tolerance zone is generally oriented to one or more datums. Profile of a line is used where it is not necessary to control the profile of the entire feature. Symbol Specifications H = Letter height H 2H H 2H Example 9-1. A feature control frame with the profi le of a line geometric characteristic symbol and datum reference. A profile of a line tolerance is used in situations where parts or objects have changing cross sections throughout the length. A pump impeller is an example of a part that has changing cross sections. Datums are used in some situations, but are not necessary when the only requirement is the profile shape taken at various cross sections. When the leader from the feature control frame extends to the related surface without any additional clarification, the profile tolerance is assumed to be bilateral. Equally disposed bilateral tolerances are equally split on each side of the basic dimensions that establish true profile. Profile of a Line between Two Points The profile tolerance can be between two given points of the object. This specification is shown by using the between symbol under the feature control frame. Any combination of letters can be used, such as “A” and “B” or “C” and “D.” The true profile is established by basic dimensions. Profile of a line is a single cross-sectional check anywhere along the intended surface. The profile tolerance is assumed to be equally disposed bilateral unless otherwise specified. This means that the profile tolerance is split equally on each side of the true profile. The actual profile of the feature is confined within the profile tolerance zone. Refer to Example 9-2. In the