Compass, Pilots Repeater Indicator Mk I RAF Ref 6A/1584, Distant Reading Compass
Here is a WWII-era Compass, Pilots Repeater Indicator Mk I Stores Ref 6A/1584, a component of the Distant Reading Compass system, as use in early versions of large British RAF aircraft such as the Avro Lancaster, Vickers Wellington, and Short Sunderland (see image showing the location of the indicator from the Lancaster Pilots Notes from 1944). The serial number is evidence of it's year of manufacture of 1941.
Here's a bit of history from the Rochester Avionics Archive:
The Distant Reading Compass was standard equipment in most multi-engined aircraft in the RAF throughout World War II until it was replaced by the Sperry ‘Gyrosyn’ compass. It consists of a master unit containing both the gyro and magnetic elements normally stowed in a part of the aircraft away from large masses of magnetic material which would distort the Earth’s magnetic field. This master unit feeds, through an electrical transmission system, repeater compass cards on the pilot’s and navigator’s panels and wherever heading indications are required. The complete compass system operates from the aircraft 24 V DC supply. The pilot or navigator has control switches for starting and stopping the master unit and a variation setting corrector control to adjust the repeaters to read true instead of magnetic heading. A complete system comprises a master unit, variation setting corrector, a control switch box and a number of repeaters. The master unit holds the magnetic element, the gyroscope, the monitoring and follow-up mechanism and the transmitter for operating the repeaters. The complete assembly is suspended in gimbals.
The system uses an electric magnetic inductor element fixed to the aircraft in azimuth which detects the direction of the Earth’s magnetic field relative to the aircraft and transmits this information electrically to the gyro element.
The D.R. Compass was developed by the Automatic Telephone and Electric Company (in 1961 merged with Ericsson Telecommunications and Plessey to form Plessey Telecommunications) and the Royal Aircraft Establishment from a model originally produced by the Air Ministry and S.G. Brown Ltd in 1934.
Some 30,000 of these instruments were made at the A.T.& E. Strowger Works in Liverpool during the WWII years.
The compass card containing the markings of the compass rotated to indicate magnetic north as it received signals from the master unit (in the Lanc, the master unit was located aft). The knob rotates the single line arrow, likely to set the desired course heading. The parallel lines actually are printed on inner plexiglas plate below the outer glass. The knob has a small spring-loaded button in its center, perhaps to engage the plexiglas beneath the glass and rotate the parallel line toward a heading. The button depresses, but does nothing in this example.
It is clearly 'experienced' but in very good condition given its age. Measures 4.5 inches square and ~3 inches deep.