Hi @cgepner,
for _DimCreaseAngle, you do not have to set a CPlane and usually for measurements you could do this without changing CPlane. To measure the angle of the border edges (of the 2 touching planar surfaces), you might just extract the edge lines using _DupEdge, make sure they are linear (your’s where not, i used _SimplifyCrv on them) and while keeping both lines selected, run _Angle and choose the _TwoObjects command line option to print the angle.
For drawing angle dimensions, CPlane should be set. In your case you might use _CPlane _3Point and click the origin where the edges meet, then X and Y somewhere on the edge as shown below. Then you can make eg. an arc which you can pick with the _DimAngle command.
To set back the CPlane, use _CPlane _Undo.,.
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c.