It was built by the greeks over 2000 years ago and is a complex series of gears used for astronomy. I learned about it in a link from an imaging publication because they used a CT scanner to fully assess it.
http://www.nytimes.com/2006/11/29/scien ... epage&_r=0
Remember this was made over 2000 years agoThe gear teeth were in the form of equilateral triangles with an average circular pitch of 1.6 mm, an average wheel thickness of 1.4 mm and an average air gap between gears of 1.2 mm.

