Symmetry has been a misunderstood and misused geometric tolerance. Symmetry controls derived median points, which are difficult to inspect and have few practical applications. Many designs require that features be symmetric, both position and profile can achieve this and are easier to inspect. Which you choose depends on the application:
Application: Control of Center Plane To control the center plane put a position control on the center plane of the part:
Application: Control of the surface boundary for clearance fit To control the surface boundary on a clearance fit, use position at Maximum Material Condition. The virtual condition boundaries are centered on datum A. Note: In this example, the feature violates the boundary.
Application: Control of surfaces To control surfaces, use profile of a surface. The profile boundaries are centered on datum A. Note: In this example, the feature violates the boundary.
