1. Start with a blank 3x5 index card. Be sure to use one that is not lined on either side.
2. Find the exact center of the card by placing a ruler or other straightedge along each long diagonal. Don't draw on the card; instead, make a small indentation where the two diagonals cross.
3. Place the card so that its longer side is vertical: Starting on the left edge of the card, go about a third of the way down the card from the top (you can estimate this distance) and cut a straight line from the edge to a point halfway across the card- that is, a point directly above the center indentation you made.
4. Again starting on the left edge, go a third of the way up the card from the bottom and cut a straight line from the left edge to a point halfway across the card.
5. Now from the right side, cut a straight line from the midpoint of the right edge to the center of the card.
6. Holding the card with both hands and keeping it parallel to the floor, twist the lower half of the card 180° clockwise so that both the top and bottom are parallel to the floor. Crease all the folds and pull the tab up so it stands away from the remainder of the card.
One of my students at Handley took the Mobius Card one step further:
