How do you test old style pcv ?

I understand how it works but just could not find a spec to test when it “pulls open.” After all the dialogue- I now assume there is no spring or spec. thank you!
because every engine, even factory fresh, is never exactly the same as as the one next to it. the factory valves were probably a "best average" type of guess. whether you use one of these or not, there's some interesting info HERE