If we're working with historic equipment then we've got to be prepared
to at least understand old units and also for the likelyhood that these
units may not be exact from one country to another. We take
international standardization for granted these days but its a
relatively recent invention, certainly post Baroque. (I might stand
corrected but this whole metric thing is Napoleon's legacy to the
world.)(He also started this practice of driving on the right.)
Stones weigh 14 pounds, there's 2 of them to a quarter and four quarters
to a hundredweight (which actually weighs 112lbs), and 20 hundredweights
to a ton (which isn't far off a metric tonne).
There are all sorts of traditional units but the only one that stumps
most of us is oil -- we all know how much a barrel of oil costs but
relatively few of us know how big that barrel is (~169 liters or about
40 US gallons).
Anyway, thanks to the Internet we're never completely stumped, but even
so sorry for the jargon.