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The Most Important Control in GD&T is Location, Location, Location
(In accordance with Y14.5M-1994 standard)

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Once datums have been established, other features must be located with respect to the datums.  Often those applying GD&T will use orientation (perpendicularity, parallelism or angularity) and form (straightness, flatness, circularity or cylindricity) controls and forget to control the location.  Features are located geometrically using profile of a surface, position and, as last month’s Tip explained, sometimes runout (circular or total).  These locating controls automatically provide orientation and, with the exception of position, form control.  Form is provided by the size dimension when using position.  The orientation and form controls should only be pulled out of the toolbox to be used as refinements.  The geometric controls shown in blue come for "free" with the general Profile of a Surface.

Back to Tips Tip added Jun 1999