Does anyone know how you calculate how much weight you are lifting when you use the machines at the gym? I've been told that each plate weighs 15lbs. If I am lifting #2 (the top plate) I assume I am lifting 15lbs. If I put the pin into the next plate (#3), then does it stand to reason that I am now lifting 30 lbs? and then 45 lbs and so on for each plate added?

I know that important thing is to watch my progress and ultimately, it's not the weight itself but the progression from 2 to 3 to 4 plates, as well as an increase in reps/sets.

But I still wanna know anyway.