Full size specific gravity tester is accurate, easy to use in all temperatures. Number of floating discs show state of charge. Specific gravity levels are printed on the tough, see-through plastic body. Has one-piece rubber bulb, neoprene tip This is for checking the state of charge of a battery. The large 16-1/4" professional disc-type tester is accurate down to -40 degree F. It's easy to read and safe to use!