As I was writing a reply to Neville, the methodology became clearer, but not crystal-clear.
I find I am off-course and stop. My wheel has gone .75 of a revolution beyond the Totalizer incrementing. I should turn around without allowing my tire to spin, so when I have the Totalizer in decrement, I have .75 of a revolution before Totalizer begins counting down. That way, in my mind, I could ride back to anywhere on the course FOLLOWING THE EXACT ROUTE I RODE TO THAT POINT, and turn around to continue. That makes sense, but differs from the "select a rim reading".
If I select a rim reading, I am revolving my tire to an arbitrary location, which is different than actual revolutions. This creates inaccuracy, I believe.
What am I missing?