Here's a real life example. If Owen has 40 carbs for breakfast and we happen to be off 20% (lets say on the higher end) on the amount of carbs. With his breakfast ratio of 1:15 he would get .53 units too much. With his ISF at 400 that .53 units would drop him 213 mg/dl. On the other hand if he has 10 carbs for breakfast, and we were off 20% still, he would get .13 units too much and a drop of 53 mg/dl. Still not great, but a lot better than 200mg/dl. I know that this will change as he gets older and his ISF changes, but right now that makes for a scary situation. It's getting late and I was up early, so I hope all this math is correct. Agreed. There are many ways to manage this disease and no "right" way. What works for one family might not work for another.