Overlap?

As I understand what overlap is. What i don't understand is the difference between positive and negative overlap. I put my cam spec in and i got -50degrees of over lap, now i put a another cam spec in and ill get like positive 40 degrees over lap. If someone could just tell me the difference between the two that would be great. thanks

Here's some info I found that might help ya bud... http://www.ls1tech.com/forums/genera...cam-guide.html