I suggest waiting until we have more-powerful propulsion sources, which should happen WAY before 10000 years, and then using some big rockets to adjust the planets' periods to be more rational. Then (if you're still alive) you can buy two or three cheap gears anywhere, thus saving lots of money and trouble. Since this is a specific suggestion, I claim the Grand Prize of $1. Please remit. Steve Gray ----- Original Message ----- From: Danny Hillis To: math-fun Sent: Saturday, February 05, 2005 1:38 PM Subject: [math-fun] 10,000 year gear train I am building a mechanical clock that is intended to show the position of the visible planets and the phase of the moon over the next ten thousand years. Thus, I would like a gear train that computes all the following ratios using a small number of gears.