Noxx,
If I understand your question right, the answer is yes.
When you apply the acid to the streaks on the touchstone, you are looking for the amount of attack, the rate of attack, and the color produced. Stronger or weaker nitric will effect these. It's a visual thing. You compare these unknown streaks, side by side, at the same time, with streaks made with gold of known karats, usually from gold testing needles or from gold objects that you know the karat of. It's really pretty simple, once you get the hang of it. Play with it. Make streaks with different things and try all the acids on them. Be very careful not to cross contaminate the acids.
Where are you in Quebec? I was stationed in the Air Force, for 3 years, near Caribou, Maine, about 40 miles from Quebec. Spent most of my time off in Quebec. Beautiful but cold. Went to the winter carnival in Quebec City one year. Great fun. Beautiful women.
