IMPORTANT Gauge and face are filled with liquid glycerin to dampen "soften" vibration and reduce needle fluctuations (also extends gauge life). Air bubble in face in NORMAL and needs to be there for gauge to work properly. (liquid may be replaced if loss occurs, use only Marlin approved glycerin - do not overfill, leave a bubble about the size of a penny). Gauge is calibrated 0 to 60 or 0 to 100 by tens in 2-lb. increments. For plastic lens clean with a good car wax or plastic cleaner.