2D or 3D dimension? That tis the question.

Hi everyone, just a quick question. I am measuring the top of the pinion bore, with points in 8 places around the outside and inside (marked in red), to measure the thickness between them, and see if the core is moving, because on the casting itself you can very clearly see that one side is super thin, and the other super thick. I currently have the distance dimensions between the points set as 3D dimensions, and have made sure that the point vectors on opposing sides line up. The supervisor, insists that every dimension, especially wall thicknesses, should ALWAYS be 2D.

Can someone please explain what should be used in this case, and why? I've also noticed that in some cases 3D works better than 2D...meaning not so screwy Luie. I do understand that 3D measures the distance from centroid to centroid, and 2D measures the features perpendicular to the current workplane, but can someone explain this a little more for me?

Thanks much