Abstract: A barometric meter such as barometer or a barometric altimeter comprises a vacuum chamber having a movable portion which displaces in proportion to air pressure. An aperture plate for allowing a light beam to pass therethrough is mounted to the movable portion of the vacuum chamber, and a light source stationary relative to the vacuum chamber is provided for illuminating the aperture plate. A photoelectric position detector disposed on the other side of the light source relative to the aperture plate and stationary to the vacuum chamber is provided for receiving the light beam which passes through the aperture in the aperture plate and for supplying an output indicative of the positional change of the light beam impinging on the photo-electric position detector. The output of the detector may be digitally displayed on a display as either air pressure or altitude.