Abstract: An electric switch actuated in response to a condition, such as the occurrence of a particular pressure level, is shown to comprise a base having a switch receiving chamber and having an open end closed by a snap-acting diaphragm assembly. A motion transfer pin is slidably mounted between the diaphragm and a movable contact arm to transfer motion from the diaphragm to the arm. The diaphragm is supported on an annular plate used to prevent over pressures from deleteriously effecting the diaphragm and may be used in forming and calibrating the diaphragm for snapping in one direction. An adjustable spring is disposed on the other side of the diaphragm to permit calibration adjustment of the diaphragm for snapping in the opposite direction. The spring is mounted in a housing adapted to be connected to a pressure source. The switch is weatherproofed by providing a skirt which depends from the housing and extends toward and beyond the base.