Abstract: A pressure switch having a movable bellows (14) in a pressure chamber (12), a first electrical contact (16) movable with the bellows, a three-dimensional cam (18) and a second electrical contact (20) resiliently biased to follow the cam. In the preferred embodiment of the invention, the cam has a radius that linearly increases with the angular position of the cam, and is tapered toward one end for all regions about its periphery except at a point of maximum radius. Calibration at low pressure is effected by rotating the cam to its maximum-radius point, applying a standard low pressure to the chamber (12) and rotating the chamber about a threaded coupling (26) until the contacts (16) and (20) are at the point of closing. Calibration at high pressure is effected by rotating the cam to its minimum-radius point, applying a standard high pressure to the chamber, and adjusting the axial position of the cam until the contacts are at the point of closing.