npk

So this question is perhaps pretty basic and I have an idea as to the answer if my assumptions are correct, but when someone advises for something like a 9-9-9 NPK ratio fertilizer, is that all in percent volume? For example, 9% of the bottle is Nitrogen, 9% is Phosphorus, 9% Potassium? I assume...

I have a quick question? When trying to figure the NPK values when making fertilizer cakes do you use zero values for parts that are used that have no NPK value? Like adding lime or flour to the mix. Do you exclude them from the calculation? It seems to me you would just use zero values as...