The unique Tank Up Coffee Mug features a printed heat sensitive gauge which is designed to resemble an automobile gas gauge. As hot liquid is pored into the mug the gauge turns red and gradually rises from the bottom to indicate how hot the liquid is. The gauge itself is the entertaining aspect of the product. Fill your mug with the hot beverage of your choice and watch the gauge climb all the way to the full mark. Its not magic, its just awesome heat-sensitive printing.