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I've never understood the desire to have a propane tank gauge.
Most gauges of this type are wildly inaccurate and if the gauge tells you that the gas is too low for your grilling but not empty what are your options? Do you waste the propane that is in the current tank getting a replacement? For the cost of the gauge you can have a full backup tank at the ready and the second tank pays for itself when you figure in the cost accocated with the waste.
Am I missing something?