Fuel Quantity Indicator, AN-F-48,-58 Fuels, US Army Air Force, KB-29P Aerial Refueling
Here is a very interesting dual-fuel, Fuel Quantity Indicator, made by Minneapolis-Honeywell part number G700C33 for the US Army Air Force order with a BAC prefix (Boeing Aircraft Corporation) for a Boeing KB-29P Aerial Refueling Aircraft. The KB-29P (116 of them) were created starting in 1948 from modified B-29 bombers, which pioneered the way for future designs of aerial refueling aircraft.
The indicator is specifically part of the refueling system, and displays fuel quantity on the refueling panel at the flight engineers station (see photo of the panel and location of the indicator from the KB-29P Flight Manual dated 1951). It displays total fuel on two different scales, depending upon the type of fuel being carried, which would likely be determined by the type of aircraft to be refueled on a mission. If the fuel was AN-F-48 (aka Avgas, eventually designated MIL-F-5752), the indicator displayed total fuel quantity up to 16,200 lbs. If the fuel was AN-F-58 (eventually designated MIL-F-5624, aka J-3 jet fuel), the indicator displayed total fuel quantity up to 17,800 lbs. SInce the volume within the aircraft's fuel system was fixed (i.e., the total gallons which could be contained), the difference between the totals is the difference in density of the two fuel types. The total capacities on the indicator are consistent with the capacity of the KB-29P's forward bomb-bay fuel tank (see photo of tank capacities from the KB-29P Flight Manual).
It is in exceptional condition for its age. The glass and case are intact, and the lettering is perfect. The instrument has a test button at the bottom right corner to check the functioning of the indicator. Measures 3.25 inches diameter by ~6 inches deep.