Attitude Indicator, ARU 2B/A, US Air Force
This is a Cold War / Vietnam War era Attitude Indicator type ARU-2B/A, made by Sperry, part number 1784163-901, MIL-I-27193A. This instrument appeared on the pilot's and co-pilot's instrument panel of a number of US Air Force and US Navy aircraft such as the Lockheed C-130 Hercules Transport. This unit has a service label from McClellan Air Force Base in Sacramento CA dated 1987.
The purpose of the instrument is to rapidly indicate to the pilot the attitude, or relationship, of the aircraft with respect to horizon, showing whether the aircraft is climbing, diving, or banking left or right, and to what degree. This model also has a small floating-ball turn/bank indicator at the bottom of the instrument. Specifications for the MIL-"C" version can be downloaded here.
The instrument is 'experienced' but still shows well. The unit requires the correct electrical input in order for the knob and sphere to function. Measures 5 inches square and ~8.5 inches deep.