This SAE Aerospace Information Report (AIR) is concerned only with aspects directly relating to available accuracy. While well-designed photoelectric, inductive or capacitive readers and pressure regulators, and other accessories are highly desirable for convenience and production rate, they are considered to be outside the scope of this AIR. This AIR is intended to define three classes of barometers, working, reference and transfer and some aspects of their use so that altimeters and air data transducers calibrated aginst working barometers will be comparable. An accuracy of ?.003 inch (or ?.076 mm) Hg should be approachable with working barometers meeting the recommendations in this AIR.