I guess I am just a bit fussy.... but I actually measure the weight of my propane tank(s) at the beginning of the trek, and again at the end to give me a good indication of my "typical" usage (boondocking, running the fridge during the trip up/back, cooking, water heater, stove, furnace). Amazing how long a 40 lb tank lasts!. The propane tank "gauge" (shown above in previous post) is ok in general, but keep in mind it is a "pressure" gauge, and as such does not tell you level in the tanks. Pressure in a propane tank is virtually constant during use, until the very end (when the gauge will start dropping). Better have your spare tank ready at this point... No grace period. Only real way to gauge the contents is either by magnetic gauge that senses the liquid/vapor level line, or by weight, which is a bit more involved, since you have to remove the tank from the bracket to accurately weigh it (I use a 50# digital fishing scale...glad to be able to at least be able to use it to weigh "something" on my fishing trips!!!).
(Oh, and where did you get that gauge for 9.99? Lowest price I found was 16.99, and that was for a very "cheap looking" version.)
2004 Jay Flight 21FB
2001 Yukon SLT