Ever wondered where to start when first setting up a pressure button..? Try this idea..
Push the button down on a set of kitchen scales and note the point where the plunger just starts to slide into the barrel. Now adjust the buttons spring compression so that at this point the kitchen scale is reading 10-15 ounces (around 280-430 grammes).
Remember, always to avoid having a stiff button spring. Too hard is obvious but too soft and the plunger may slide right into the barrel and your soft spring then becomes a very stiff one.