Hi Bev,
My guess is that you would get it more accurate without a measuring device  you could measure two of the vertices reasonably accurately, but I don't see how to find the other two. Here's how I would do it. Hold your fingers at the eight vertices of a cube  you should position your finger tips so they form the six square faces. You get four evenly spaced points by choosing every second vertex of your cube (so that any two of the chosen points are diagonally opposite vertices of a face of the cube).
Chris
