As soon as I got home, my wife told me that our son at his university had gotten a stick in his chain and needed help with it. I figured that the DR was jammed up so I grabbed a few tools and rolled back out. As it turned out, he'd snapped his DR hanger somehow. So cutting his chain for single speed operation, I got it a hair too short for the right chain line which was a little annoying in practice but good enough to ride home with.