Cylinder Head Temperature Indicator, Type B-7, US Army Air Corps Pre-WWII B-25 It is a hand held

It is a hand held finder used to ascertain the range of an enemy aircraft based upon its known wingspan

was a component of the SCR-280-A Radio Compass System

it has a knob to adjust for barometric pressure

25 inches diameter by ~2 inches deep

Cylinder Head Temperature Indicator, Type B-7, US Army Air Corps Pre-WWII B-25 It is a hand heldThis is a pre WWII Type B 7 Cylinder Head Temperature Indicator as used in aircraft of the US Army Air Corps before and during WWII. The indicator measures the temperature of the cylinder head via thermocouple from a single engine, from 0 350 deg C. The B 7 indicator had an integral light source in the upper right corner, although the bulb is missing from this example. Made by Weston, part number 86884, with a serial number prefix of AC 39, evidence