How can I Make a Simple Timer?

A timer can be made from two plastic cups and some sand. Place first cup upside down on table and second one on top right side up so bottoms of the two cups are touching. Punch a hole through the two cups where they meet. Measure out some sand and using a stopwatch, let the sand pour through. Add and take away sand until you have one minute's worth of sand. Make top and bottom for the plastic cups from a piece of cardboard fastened to cup rims.