Palmer Mfg. has several different ways to show the level of the contents in your tank. These range from the simplest of calibration strips that are integrated into the tank wall with a sight glass, to the complexity of gauge boards to give an electronic readout. The two most requested types of level indication are the calibration strip and the sight glass. The calibration strip is in gallons.
The strip is integrally placed into the tank wall to allow for visual verification of the amount of liquid in your tank. Increments vary from 10 gallons to 100 gallons. The sight glass works in the same manner that the calibration strip does; in fact, the sight glass comes with a calibration strip. The sight glass has actual liquid in it to give a quick visual of the amount of liquid in the tank. There is a valve located at the lowest fitting so that the sight glass can be "turned off" and a drain valve at the bottom.