The pitot static system consists of the instruments used for determining aircraft’s speed, altitude, and altitude trend (or change in altitude).
These instruments generally consist of the altimeter, airspeed indicator and vertical speed indicator. The system utilizes air pressure differences to provide the pilot specific information. The static air pressure port provides baseline air pressure. This pressure is used for the altimeter. A pitot tube outside the aircraft receives air pressure due to forward flight, or ram air. This pressure is compared to the static pressure and the difference is displayed as airspeed. The vertical speed instrument uses the static pressure and a calibrated leak. The rate of change is indicated as climb or decent.
FAA-H-8083-25B Pilots Handbook of Aeronautical Knowledge pg. 8-1