This Aeronautical Standard covers two (2) basic types of instruments as follows:

TYPE I - Range 35,000 feet. Barometric Pressure. Scale range at least 28.1 - 30.99 inches of mercury (946-1049 millibars). May include markers working in conjunction with the Barometric Pressure Scale to indicate pressure altitude.

TYPE II - Range 50,000 feet. Barometric Pressure. Scale range at least 28.1 - 30.99 inches of mercury (946-1049 millibars). May include markers working in conjunction with the Barometric Pressure Scale to indicate pressure altitude.