Ultra-Low Differential switch can be activated by 0.005″ W.C. and up. It is the most sensitive simple diaphragm switch obtainable. It has a dial setting that is calibrated for each unit to a primary standard. Many users connect a lamp load across the contacts and use it as a low cost means of determining what value of inches of water column they have in their system. This lowest range switch does not use a micro switch. It uses an electronic circuit where the load can be 8 amperes, 120 volts, 60 AC. The load is connected in series with the power source and then connected across the switch terminals. Custom built units with N. C. gold contacts for use with low voltage and current are available. Switches with higher operating ranges use micro switches. This switch can be custom built without housing, etc. to obtain minimum cost for large quantity applications.