I'll let someone who knows how to present a video do it, but the simple version is to put the pressurized second stage faceplate down into a bucket of water slowly and look at the water level on the reg when it just starts to hiss. The depth of the diaphragm below that water level is your cracking effort.That would be cool. Closest I got is,
Alec Peirce showing how to use a Magnehelic:
And a DIY thread here for making a Slanted U-Tube Manometer from a fish tank hose & some wood:
DIY Magnehelic Gauge
What regs are you diving, if I may ask?