Okay, thank you, that helped a LOT, actually. This project has become somewhat extended. When I tried to overlay an Earth Map onto my nice FR Mercator map weird things happened - I didn't realize there were different formats.

I am going to assume your grid is a precise Mercator, so if I find an Earth Mercator map, all the lines should lineup perfectly, correct?

(And thanks again for all of this - its a great resource!)