Mr McCreary, that homemade injection tester is very impressive. I think that it is the best that I have seen. I hereby award you the official TwitchKitty Keep it Simple design award for simplicity bordering on elegance, congratulations. Keep up the good work.

In the manual (FSM) there is one test that requires you to close the valve to the gauge. If you refine your design you may want to incorporate that feature.