These are fundamental for 3D work. Setting a Working Plane allows you to work directly…
Vectorworks Tip #207 – Working Planes with Dimensions
Sometimes when you place a dimension, the dimension snaps to objects that you are not intending it to. In this image you can see how the dimension has snapped to the front of one object and to the rear of the other giving me a measurement of the distance between the two objects, but not the one I want. If you set your Active Plane to Screen Plane, you can measure the distance between the two objects on the screen plane, which might be the dimension you are looking for.