I'm on Levimir and Humulog insulins. I'm doing carb ratio and have no problem with that. However my doc suggested that if the blood sugar is high or low, to adjust the dosage slightly at mealtimes accordingly. I'm not a fan of guessing and found a nice iphone app that will do it for me. But you have to put in a correction factor. I've been playing around with that number but wondered if there was actually a scientific calculation at arriving with a proper correction factor.