I tried making a mobeus strip (by taking a strip of paper, and turning it 180 degrees then connecting the edges). I drew a line on the strip prior to turning it and connecting the edges. The line appeared on one side and not the other...which is inconsisstent with the fact that a mobeus strip is supposed to have one side only. Mine had two. How do I make one--accurately? Why does it have only 1 side? How does this happen? How does it work exactly (not how its made please)?