Gyrosyn Compass Master Indicator CL2 Sperry RAF Avro Shackleton, English Electric Canberra

This is a Gyrosyn Compass Master Indicator Type C.L.2, made by Sperry, as used in large aircraft in both British military and civil service during the 1950's in Reconnaissance/Bomber aircraft such as the Avro Shackleton and English Electric Canberra, see description below. See photos of its placement at the navigators station in the Avro Shackleton and Canberra. It was also placed in passenger aircraft of the BOAC, according to archival documents, but I've not located any specific photo references.     Measures 5.75in diameter and ~10in deep, and rather heavy. It is in terrific condition given its age.  The dial markings are clear and the glass and case are intact. The center knob "Autopilot" rotates and centers on a detent, but its function must require the correct electrical input.  The Variation Setting knob rotates the card within the small window north of center. There is a thin sliding ring around the dial to which a small triangular pointer is attached, and opposite of the poin