Suzy, one thing I can tell you about this roller coaster ride is that you can't get excited about those numbers - unless they're way low - in the lime greens - then you can get excited because that's where the dangerous stuff is...however pinks and reds and even blacks...well that's Feline Diabetes running it's course...
Our kitties don't have a normal endocrine system making normal amounts of insulin to help regulate the sugar in their blood streams - so those numbers are valuable only to allow you to know that things are out of whack....So as Chris mentioned above the 300's are just that a range of numbers...same for the 400's and 500's....if you kinda step back and look at the ranges you might handle it easier than trying to focus on an exact number at a given hour - however, this rule does not apply to lime green numbers - those numbers are much more telling and hypoglycemia is where you want to react...and quickly...
I hope this is helpful and will help you relax a bit while on this journey...