The three standard types of gauge glass are listed: Type A, Plain is designed for moderate-pressure steam boilers and liquid level indicators. Type A, High Pressure is controlled to tighter flatness tolerances to be used in higher pressure applications. Type B, Reflex is made for ease in determining liquid levels, especially in clear fluids. The glass has vertical prisms extending the full viewing length of the glass. The prism side faces the liquid, and the sections of the prisms not covered in liquid reflect light brilliantly. The sections covered by liquids appear dark in contrast.