Abstract: A differential pressure switch assembly for low pressure applications permitting accurate "in field" set pointing of same, comprising a capsulized instrument that includes housing high and low pressure sections defining in assembled relation a pressure cavity across which such sections mount a flexible diaphragm separating high and low pressure chambers, with the low pressure section mounting at a site on the low pressure section a snap switch unit of a size appropriate for such assembly, which unit has a projecting plunger therefor that has an end portion disposed in the low pressure chamber of the unit, with the assembly further comprising a pressure differential sensor disposed for effecting electrical switching of the snap switch unit when the pressure of the assembly high pressure chamber exceeds that of the low pressure chamber by a predetermined differential.