Understanding the Correct Usage of Dashed Datum Targets in Drawings. There are some things I never learned in school, but that I picked up on the job. One of them is the proper use of dashed datum targets in technical drawings. Today, I want to share what I’ve learned, using a 3D model I created of a base plate for longboard trucks to illustrate the concept.

The pink datum point (A2) is on the top surface of the baseplate, while the green datum point (A1) is on the bottom surface.

In a 2D drawing, a datum target is used to call out a datum point. For a datum point on a visible surface, we use a standard datum target. For a datum point on the opposite side or a non visible surface, we use a dashed datum target.

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Dashed datum targets are not to be used in section views.