What I do is take a bathroom scale and set it on the drill press table. Then use the drill press to compress the spring. It is an easy way to check the load at different compression levels.
Another interesting thing. It is a good idea to take a new spring and check it. Then compare it to what you are running.
Example: You are running a 130/300 primary spring. You purchase a new 120/320 primary spring. You switch them and you don't get the results you expected. After checking the new spring it is actually running more like a 120/305. So you can really chase your tail if you don't know exactly what your new spring is compaired your old spring.