Fuel Mixture (Fuel-Air Ratio) Indicator, Dual Engine Type B-6A

This is an early WWII-era Fuel Mixture (Fuel/Air Ratio) Indicator used in early twin-engine aircraft of the US Army Air Corps.  Examples of aircraft which used this indicator are versions of the C-47 Skytrain transport, C-45 Expeditor, and A-29 Hudson bomber. See illustration of the location of the indicator on the panel of the C-45 from its flight manual dated 1944. 

Per the attached spec sheet, the instrument was a component of the fuel mixture analysis system, which continuously analyzes the exhaust gases of the engines to determine the proportion of gasoline and air in the fuel mixture entering the engine.  Through its use the pilot is enabled to set the carburetor mixture controls so that the mixture is not lean enough to injure the engine and not rich enough to cause high fuel consumption.  

The fuel/air ratio is displayed for the left engine on the upper scale, and the right engine is on the lower scale.  Fuel mixture is rich when the pointer moves left, and lean when it moves right. 

AC US ARMY is embossed in the lower edge of the face, below the FUEL/AIR RATIO. This indicator has a serial number prefix of AF 43, evidence of a year of manufacture of 1943.  

The indicator is in very good condition given its age. The dial glass is clear and the markings are precise. Measures 3.25 inches diameter and ~4 inches long.