I'm developing this app, which I want to support both units, so I've read up on both units. But I got to thinking, and my wife confirmed this, that many people, even health professionals, are intimate with the one unit but know nothing about the other.
Starting from basics, both units are used to measure the same thing. This is like miles and kilometers. HBA1C is measuring something different. So there is a relationship between the two units, which is basically:
1 mmol/l = 18 mg/dl
So, to give an example, I've talked about blood sugars of 15 mmol/l in the past (I'm almost half that now!) - this is 270 mg / dl. My current average is 8.9 ± 1.4 mmol/l - I might say more about that in a later post - which is 160 ± 25 mg/dl. So clearly, above that of a non-diabetic, but getting better. As I'm starting to work with this new unit, I'm finding it quite convenient, and in fact I've changed my app to store the numbers, internally, as mg/dl. although, of course, it is just a number. Each number in the database carries with it some crazy-silly precision, so 10 or 200 doesn't make any difference to it.