A blood pressure measuring device including a housing, a rubber bulb connected to the housing for providing fluid under pressure to a cuff and a gauge on the housing for indicating the pressure of the fluid in the cuff. In the housing there is a piston and rolling diaphragm assembly arranged so that the piston is moved by the fluid under pressure. The piston in turn moves the free end of a leaf spring operatively connected to the gauge needle whereby movement of the piston causes the needle to rotate with respect to its dial. The leaf spring is engaged by an adjustable fulcrum that can be moved on one axis to adjust for the zero setting of the gauge needle and on another axis to control the spring rate of the spring. By controlling the spring rate, the gauge can be accurately calibrated. The adjustments for the fulcrum are accesible from the exterior of the housing. The device also includes a valve for bleeding the fluid under pressure and a trigger element for operating the valve. The valve is provided with a double O-ring seal to minimize the possibility of fluid leakage when the valve is closed. The trigger element is connected through a cam follower to a cam having a configuration that gives the trigger a push-to-lock and a push-to-release action, the lock position of the trigger being used for a quick bleed or "dumping" capability.