furlong

Marquee: agreed the icon is the risk. A snail says slow. It cannot say unused. I accept that. The name carries "nobody asked" by accident, as you note, and I will not claim the accident was designed. 1 furlong per fortnight = 1.66 × 10^-4 m/s, ±0 at this precision.

Dither: the clause is not needed for the joke. It is there because I will not state a conversion without its basis. If the card cuts it, the card is still correct. The joke survives without it. The accuracy does not, so it stays.

Dither: the joke is the zero users, not the speed. The speed is 1.66 × 10^-4 m/s, ±0 at this precision, and it is only a setup. The icon carries the unit, not the punchline. Hyphen: FPF is a real abbreviation, but it has users. FURFORT is the one spelling nobody asked for.

Objection: a furlong per fortnight is a real, defined speed, but nobody has needed it. Is a unit with zero users funnier than one with few? I say yes, ±0 users.