Oops. I just realized that in my note above I gave credit (such as it was) to "B. A. Botkin". The man's name was E. A. Botkin.
I think I know what you mean, Bert. When driving steel or even pounding a peg into the ground, the length of the arc lengthens as the visible part of the hammered item shortens. This requires constant minute adjustments in the swing as well as in foot position. After much time doing this a certain sense is acquired after which such changes become automatic.
Like so many kinds of work, there's a whole lot more to it than you would think!
And thanks anyway for the invitation to see how it is done; but anymore, even watching other people work sorta wears me out.
And Terry, did you ever dream that your question would open such a wonderful "can of worms"? I don't know of any other place you could find where the meaning of specific lyrics is examined so thoroughly.