Oh, no, I'm pretty sure about this one. Put 2 hinges in the way I mentioned and watch the motion of the surface, the moving surface's edge moves against the stationary's edge on the axis. It moves such that if you hold the stationary part stationary the two edge's are always in contact _at the same point on the stationary edge_. If you do it vice-versa the edge of the moving surface is actually moving up and down, not at all like a real plane. Its hard to visualize unless you're looking right at it, hence it took till my 5th hinge to get it.