The scales are the same. The number is a percentage. I just looked it up and the test accuracy is about +/-0.5. So if you went from 7 to 6.4, it's likely just a small improvement and don't freak out if the next is 6.8. If you really want to understand if you're diabetic, a glucose challenge is a good test. I get the impression that many doctors don't know how to interpret it and it requires you to hang out around a lab so they can test multiple times over ~2hours. If you're A1c is mid 6s to 7, you're certainly not as healthy as you should be. You may want to find a nutritionist that has a success record of reversing T2D