Lynn, This was pretty obvious when I first started taking pictures with it, every was out of focus, and every once in a blue moon one would be sharp. Mind you, it wasn't terrible but it was obvious. My 70-200 looked perfect at 0 and -3 just made it look a little better.
As for FoCal, it's a software program that analyizes pictures of a target it takes when connected to a computer and then has you adjust the focus. There are a few threads on it over on the D800 forum.
I would expect some level of variance from lens to lens, +/- 5 would be acceptable, but I was just a bit puzzled by a $1900 lens being -16.