I send my boss a home and subpage design for a website. Both have exactly the same pixel width...

Boss: Your homepage is wider than you sub.

Me: I sent you an image where one is right below the other so you can see that the width is exactly the same.

Boss: Well it's not. I'm telling you it's obvious that its not.

Me: If you just look at that image where one is right below the other you'll see that they are the same width...

Boss: Here look I'll prove you wrong.
She takes out a RULER. She spends about 10 minutes measuring each image on her LCD. After much debate with herself....

Boss: You're right they are the same, my screen must be messed up.