Gauges give an approximation of fuel left inside the tank, and therefore aren't exact and at times, although not often, can fail. The gauge you see on the outside of your tank with numbers indicating what percentage is in your tank is actually part of a float assembly that is hard at work inside your tank.
Under your external face gauge is a stem that extends down into the liquid propane in your tank. At the end of that stem is float that raises and lowers when your tank is filled and when you use propane, respectively. As the float moves up and down, it turns a pinion gear that will move the gear in the shaft, which will in turn move the needle on your external face gauge letting you know about what percentage is left in your tank.
Float systems can be found all over your home - most notably in your bathrooms and sump pumps. Anyone who's experienced a flooded basement or toilet knows the sting (both financial and messy) of a failed float system. Luckily though, floats in our propane tanks tend to be consistently reliable and our service team members are experts at fixing or diagnosing issues when they aren't.
Let us know if you ever have any questions and try to remember to call early when you need a delivery.