It isn't just blood glucose measurement units that differ. The USA (and maybe other places) have some weird and wonderful measurement units for other blood markers, too.
For me, unscientific and fairly innumerate as I am, the initial shocking surprise of realising I was travelling fast in the direction of diabetes was made much more difficult by the variety of numbers being quoted. What a confusing nightmare! I started out with an HbA1c (of 41), which term I somehow found impossible to get into my head, because I had for a long time no idea that Hb=haemoglobin. Then I began reading books and because the best ones were American, HbA1c was quoted as eg 7%. Then I began testing and found the numbers on my meter were expressed in mmols/L (eg 7.0) and seemed to bear no relation to my A1c of 41 or to the meter readings mentioned in books as mgd/dl (eg 100).
When I read I tend to hear the words in my head, but mgd/dl forms a kind of stumbling block, an indigestible hiccup in my mind. OK, I have learned to multiply and divide by 18 when reading my favourite diabetes texts, but it's still an extra layer of fog to have to peer through. As for the A1c, I have in front of me a printout from a helpful chart by Diabetes.co.uk showing a sort of rainbow where I can more or less see that my 41 is a bit worse than 6% and maybe a bit worse than 7mmol/L home readings, but not as bad as 42, which is definitely worse than 6% in America and 7.0 on my meter. And I have identified that the A1c I'd like but will probably never attain is 31 ie a bit worse than 5% and 5.4. I daresay in a bit the European Union, or the UK NHS, or President Trump will decide that actually they'd prefer to see diabetes expressed in carats or millimetres, and off we'll go again.
I can tell you this, any time a new arrival on the Forum needs the numbers around diabetes explaining, it's no use tagging me!