The interactive figures on this site can be operated following the instructions below.

• Click and drag on red points to move them.
• Click on buttons (when displayed) inside the sketch to cause objects to move, or new objects to appear and disappear. (If a button stays down when you click it, you can click a second time to release it.)
• When objects are animating or moving, press '>' to speed up motion or '<' to slow it down.
• Press 'r' on your keyboard to reset the sketch to its initial configuration.
• If the screen becomes cluttered with traced objects, click the red 'X' (when displayed) in the lower-right corner to clear the traces.