Thanks zanglonli, your method works like a charm, measured a 17.5lbs spring as 18.0lbs, which is pretty close considering that it's quite hard to keep the pressure even to get a good reading from weights.
I imagine that it could be a bit more precise to use a fixed weight balast which you can put on top of the spring and have an opening in the middle where the caliper depth probe goes in. That way you also wouldn't need the weights each time once you know the weight of your balast piece.
-=Schumacher Cougar KF2=-
Racing in Latvia