Only two, you were lucky. We learnt using f.ps. (feet.pounds.seconds), c.g.s (centimetre.gram.seconds), m.k.s (metre.kilogram.seconds), and S.I. systems. Then all the conversions of units between them all.
Even though I taught physics for nearly 40 years I still prefer pounds per square inch to hectopascals for most measurements of pressure, Thou of an inch for clearances etc. One useful unit is the ‘gnat’s kok’ to indicate something very small, possibly too small to mention but important all the same, as in “it needs a gnat’s kok removed to fit”.
Note: 10 gnat’s kok = 1 smidgen. 10 smidgen = 1 ciggie paper. ( censor kicked in on that one).
10 ciggie paper = 1 tad.
Or the unit used by my teacher when the unit would not come into his head.....the famous "Hectarefootpint" . A very useful unit that easily combines area, length and volume in one easy to remember unit. Hes is however dead now!.....buried 1.8288 metres down!!
All of my learning was done in Imperial units - I'm no stranger to the Slug & the Poundal!
The big advantage of Imperial for educational purposes is that to find your mistake you divide your answer by the correct one or vice-versa & you get something like 12, 16, etc. Do it in Metric & you get multiples of 10!
For everyday use I prefer Metric, but when it comes down to precision stuff I have to convert to thou's to understand the fit between components & the manufacturing process used to achieve the specified tolerances.
I still find metric units more difficult to visualise - the gramme and the millimetre are too small so I find it much easier to visualise 1 foot or 12 inches than 300 mm. That may of course be familiarity but I still think in Imperial most of the time. As I'm of 1952 vintage there was little or no metric education for me at school. As for currency, a pound could be easily divided into 2,3,4,6,8,12 etc. old pence, but only into 2 or 5 new pence. If you've got three kids, how do you divide £1 equally between them? Mind you these days £1 buys so little it's not so much of an issue!
Ancient brain still defaults to Imperial, though when measuring I'm more likely to use metric, and of course our school rulers had centimetres down one side so it was always around.
The week after "conversion" in the early seventies the local timber yard insisted I order in metric, so I painstakingly converted all the dimensions of the wood needed to build a slot track. Man in yard was befuddled and said: "We have two by two or two by one."
"But you said...?"
"You have to order in 2.4 metre lengths," was his reply.
Which is still the muddled British way in some areas. Miles per litre, anyone?
Wood yards also used a unit called ‘a unit’, about 11 3/4 “. Or 30 cm. near enough! So perhaps 2.40 metres is 8 units.
I once needed a piece of glass 5 feet in length therefore I went to the local glaziers, as you do, and gave the specification to the young guy. He went and cut it and I took it home; it was 10 inches too short. I took it back and said it needed to be 5 feet and it was only 50 inches long, his reply “ that’s right it is 5 feet, there’s 10 inches to the foot”. I had a replacement cut by an older member of staff.