Because I'm just getting this website going, I'll gradually expand this page over the next few months
If you are on insulin, then you need to calculate your carbohydrate intake. Yes, you might have a calculator - but a calculator can't tell whether or not you are actually doing the right sums. And what if your calculator is faulty or you lose it?
If you still have injections rather than being on an insulin pump, then you will also need to work out the insulin necessary for the carbohydrate you have calculated - so you have to do two lots of maths.
Doing the maths of diabetes is just like any other maths you need to deal with in life. In many cases people get their sums wrong because they rush into it without taking a few seconds to think the problem through. Do not fall into that trap - approach it calmly and confidently. You can then get the maths right - and that will hopefully improve your diabetic control.