VORs, which began to proliferate after World War II, made roads — or railroad tracks — in the sky. Still, positions have two dimensions — ignoring altitude — and radials provide but one. Before radar was universal, every IFR position report had to be accompanied by an estimated time at the next fix. This required some bookkeeping; if you daydreamed, or you got out of range of the signal, or the winds became particularly capricious, it got tricky. DME solved that problem. What a neat thing it was, that slim box confidently reeling off tenths of a nautical mile! When I got a DME, I felt that I had everything I would ever need.