>> baseball

How large is one of those, even? I much prefer to work with perfectly spherical Olympic swimming pools.

Would that be the original British Imperial SOP or the closely-related but not-quite-the-same American SOP?

Actually, the American SOP is the original because the British changed the definition of the gallon in 1824, which you will notice is long after the Revolutionary War. No one in America cared, so we kept on using our customary units.

I’m British with, funnily enough, a Duke’s County cricket ball on my desk.

My nephew is Californian and I gave him one for his sixth birthday. Mine felt a bit lighter so we did an experiment over Zoom together to measure the density. He’s certainly a bit young for that — “it’s the same size but yours is heavier” — but there’s no harm in influencing them from an early age.

Of relevance to your comment: I made a point of doing it in grams and millimetres.