The equations for the swinging mouse assume that you measure from a point near the mouse's centre of mass. Here's how to find your mouse's centre of mass:

• Balance your mouse across a pencil, like the illutration to the right. Try not to let the cord interfere too much.
• When you find how far down from the cord the balance point is, make a little mark there. That should be close to the centre of mass.
• Measure from there.

(The rounded Apple mouse balances near the middle of the ball. Your mouse balance may vary.)