Brake Booster issues

How do you diagnose "fail"? To test when you have the booster out, just connect the vac hose from another car that is running. When you push in the pedal rod, the output rod should follow w/o requiring much effort to push. It might require you pushing on the output rod to return, as the MC spring does (forgot). You will hear air leak in as it moves, but should be no noticeable hissing when stationary. Being an engineer, stating any measurement w/o units is negligent, and stating the wrong units is a major error. A probe crashed on Mars ~15 yrs ago because NASA assumed a contractor's computer thrust calculation values were in "lbf", when actually "N". Both parties were grossly negligent to ASSume.