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