I think it would be nice to see the values of salt from cure as well as how much salt to add to hit the %.I'd actually have preferred they had kept both separate and added an extra box that showed total salt from the cure+ additional salt. Someone using my numbers at 1.5% salt plus the 0.25% from the cure has to already know what the calc is doing and that they have to input 1.75% in the salt value box to get my cure out of the calc.
I might not have explained it very well but the digging dog calculator will ensure you don't go over the salt % you enter.
So in your recipe if they enter your 1.5% salt it will ensure that the salt from the cure and the extra salt they tell you to use will add up to be 1.5% salt total and not go over. So it should be good, but yeah they don't call it out separately which can definitely be confusing :)