Have you ever heard of calibrating a light meter for the time of day?

I think he meant that some meters have to be adjusted. If it says "7" and you shoot at what ever 7 is, you'll probably get a picture, but it's not an art, it's just a pitcha. If the film says iso 100 on the box, it doesn't mean it's at it's best there. Or maybe it cost more than @ 50.