Cigar Aficionado gave out some nifty gauge measurers with last months issue. They are cardboard with a ruler on one side and gauges in the middle- each even size cut through. If you cannot get your hands on one, let me know, and I will see if I can scrounge one up from my shop owner.

This site has a guide that prints up nicely:

http://www.cigargroup.com/register.htm

It is the PDF file at the bottom of the page.