There are several different types of gauges that are installed in tanks, one of the most popular and difficult is a bobber type gauge. This a long glass tube with lines for full, ¾, ½, ¼, and measurements in between. Inside the tube is a bobber that represents where how much oil is in the tank, similar to the image above. Many customers will call and state that the tank is empty when the bottom of the bobber hits E. The bobber is meant to be read from the top down. So if the top of the bobber is at ¼ you have enough oil for several days in the winter, but should schedule a delivery or a delivery will be on its way. Other gauges include dials and old-time outside thermometer styles which can be easier to read off.