I am currently working with some old Autocad drawings. When I open them up in eDrawings, and try to take measurements using the measure tool, it always claims that there is a z-component to the dimension (ie. dX=27.644 in, dY=3.362in, dZ=275.59in, Dist=276.993in). This means that I have to get out my calculator (x^2 + y^2)^.5 to get the acutal planar distance (27.848in). How can this happen on a 2D drawing?
The worst part is when the z component isn't very large, and the Distance number seems reasonable so you use it, not realizing it is incorrect.