Can someone explain how that gauge works? Does it just measure pressure? I would expect the vapour pressure above the liquid level would not vary with the depth of the liquid. Otherwise the humidity in the air above a lake would depend on how deep the lake is. I would expect the pressure to vary with temperature.
Also, the gadget appears to have no outlet for propane to flow to an appliance. I guess you have to disconnect your propane bottle and attach the gadget to get a reading. I disconnect and weigh the bottle with a suitcase weigh scale.
I can smell a pretty small leak.