Key Points
Profile of a line specifies a series of 2D cross-sectional tolerance zones along the true profile, within which each 2D surface element must lie. The cross-sections are not compared to each other as a single entity. When used with datum references and as a refinement of profile of a surface (see example below), it may be necessary to clarify the cross-sections are only oriented to the referenced DRF.
Example Drawing
How to Read It
The profile of a line controls the cross-sections tighter allowing the part straightness to vary more within the larger profile of a surface.
Note
Profile of a line is not a well-defined tool in ASME Y14.5. There is some controversy over how the cross-sections of the surface are taken for evaluation. There is also controversy on how the 2D tolerance zones are established. Are the tolerance zone boundaries normal to the surface element, normal to the drawing view in which the symbol is applied, or normal to the referenced DRF? Notes or a company addendum may need to be added when using this symbol on a more complex application with varying cross-section.