Cut the floss so that you have two pieces about 15 inches long. Then, cut 14 shorter pieces: two that are 1/2 inch, eight that are 1 inch, and four that are 1 1/4 inches.
Stand the large paper clips on end by attaching them with tape to two vertical pieces of cardboard, two on each piece. These pieces of cardboard could be the ends of two shoe boxes, placed about two inches apart. These clips will be the vertical supports of your bridge.
Run the 15-inch pieces of floss over the top of both paperclips, lodging them in the top but giving some slack between the clips so that the floss hangs down between them. Make sure that there is the same amount of floss left on both ends.
Tape the short pieces of floss to both sides of a ruler, in this order, 1/2 inch, 1 inch, gap, 1-1/4 inches, 1 inch, 1-1/4 inches, gap, 1 inch, 1/2 inch. Tape the other ends of the pieces of floss to the 15-inch pieces and hang the assembly from them.