Key Points
Straightness of a median line defines a tolerance zone in which the derived median line must lie. When specified at MMC, it defines a virtual condition boundary which the surface must not violate. Note the feature control frame is placed below the size tolerance to make it a median line control. It is most common to use straightness of a median line with an MMC modifier.
Example Drawing
How to Read It
The derived median line of the feature’s actual local sizes must be within a cylindrical tolerance zone of 0.6 at MMC. As the local size departs from MMC, an increase in the local diameter of the tolerance cylinder is allowed equal to the amount of such departure. In addition, each circular element must be within the limits of size.
