Gyro Horizon Indicator, British RAF Sperry Mark 1B Japanese The knob would rotate the

The knob would rotate the face of the dial while the pointer remains fixed to set the present field elevation

as depicted in its Flight Manual (unfortunately the page showing the indicator does not photograph well)

See photo of the location of the instrument on the co-pilot's side of the instrument panel from the Flight Manual dated 1946

AC 0-15 Volts

This is a Machmeter

Gyro Horizon Indicator, British RAF Sperry Mark 1B Japanese The knob would rotate theHere is a British vacuum driven Gyro Horizon Indicator Sperry Mark 1B as used by aircraft of the Royal Air Force and British Fleet Air Arm during the 1940's and 1950's. This one has a manufacturing serial # incorporating "52", likely made in 1952. Measures 4. 5 inches diameter by 6. 5 inches long. The instrument looks terrific and would make a wonderful display piece, as long as you "Handle Like Eggs"!