Boost Pressure Indicator, MK IIIm, 6A/1581, British Royal Air Force, 1943 C-121 but I've sold 3 from

but I've sold 3 from this lot which are identical to this one including the label)

The knob itself is missing

shows a (+) positive reading indicating the current is flowing to the battery (charge)

Measures 5

and fighters P-38 Lightning and P-61 Black Widow

Boost Pressure Indicator, MK IIIm, 6A/1581, British Royal Air Force, 1943 C-121 but I've sold 3 fromHere is a WW2 era Boost Pressure Gauge, 7 to 25 PSI, used to indicate the supercharger power being delivered to the engine when demanded. Used in Merlin powered RAF, RAAF, and RCAF aircraft. According to the RAAF 346 Types and Locations of Instruments in RAAF dated 1945, the 6A 1581 appeared in the DeHavilland Mosquito. This is New Old Stock in its original box dated 1943. Mint condition gauge.