Mitch4 sends this in: “Okay, I guess I see what is meant to be a joke, just in the unlikelihood of the executioner stopping to satisfy his curiosity, or the condemned man politely offering this sort of accurate explanation. Or perhaps in the gallows humor (ahem!) of how he describes the value of the bottom half.

But I couldn’t shake the feeling this must be based on some famous incident, of history or legend. But got nowhere asking Google things like “what members of the French aristocracy after the Revolution wore bifocals?”. (Though it did see some sort of nexus through Benjamin Franklin, a century earlier.)”