I have a selection of test springs with known weights. When I say selection, I mean 3. If I'm building an outfit that is different to others I have done, I'll pick the one I think is right and try it. If it's too soft, harder spring. If it's too hard, guess what? Springs are cheap, if you build outfits or mess about with them a lot, it's a worthy investment and you can guage the exact spring that you want from the 3, rather tha ending up with something that is what someone else used, but isn't really quite what suits you. As the man said, Hagons are fantastically helpful and knowledgeable people, give them a call.