What were you doing the night of Saturday, March 19, 1977?

Like 21.2 million other Americans, I was watching the final episode of “The Mary Tyler Moore Show.” Watching it and making a nerdy audio recording of it for posterity. Sure, I didn’t anticipate the cassette keepsake having such an eardrum-assaulting HUM on it; but at least I felt like I was a part of something historic. And maybe I should use the tape’s hum even today to drown myself out when I spontaneously start singing, “It’s a long way to Tipperary, it’s a long way to go…”

But I’m getting ahead of myself. The...