Say I'm out in the shop working on a project, and I have to change a dimension on a piece of wood. I say to myself (silently though at times I might mutter out loud), Let's see, this is 100 mm long, and doesn't fit by 3 mm. I need to set the saw stop to 97." The words actually form in my mind, just as they are doing right now when I am typing this sentence.

Oh, I see you already answered this and I missed it the first time around. But are there really no mental pictures to go along with what you're muttering?