I've (I can NOW say) foolishly bought two of these 'in line' gauges, one for a fire pit and the other for BBQ tank. They both seem not very acurate. Perhaps the more expensive ones (of this species) might be more reliable??? I prefer the style I've been using for years. It is a battery
powered 'warning' system that magnetically attaches (at a predetermined place on the tank) to the side of any size propane
tank. When fuel gets to that level, this guage emits an audible beep and a small built in led light
IMHO: The other ulternative is to TRY an keep track of how much fuel you might have used (keep track of the number of times you've used the tank) and always keep one of those disposable tanks with the appropriate adapter for use when you realize (while in the middle of a great BBQ,) that your BEST GUESTIMATE of overall usage is drastically flawed!!!! LOL.