This Aeronautical Standard covers two 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.