Gauge For Propane Tanks

Any "gauge" based on pressure is useless on an LP tank. This is because, based on Boyle's gas laws, the pressure of the gaseous propane in the tank remains essentially the same until there is no more liquid propane to evaporate into gas in the cylinder. Therefore, the pressure gauges go from full to empty all at once. Scales are the best way to determine how much is left in a tank - or the warm water test. I have one of the ultrasonic "pens" that's supposed to tell me the liquid level in the tank. It's not much more reliable than warm water - and I still have to remove the tank from the bay to get a good reading. If you don't have a class A with a large, non-removable LP tank with a built-in gauge, the advice from several above on managing two tanks is the best (my regulator flips over automatically when the primary tank is empty - I just have to remember to check it every now and then!).

Rob