Positions of celestial bodies are indicated by height above the horizon and by azimuth. The direction of a celestial body to be observed can be determined with the help of an azimuth ring.
An azimuth ring like this is placed on the compass and is rotated in the direction of the celestial body to be observed. With the help of the rotatable prism, both the celestial body and the compass rose are observed. In this way the direction is determined in which the celestial body is located. Sunshades are available for sun observations. Land objects can also be observed with it.
This Azmuth ring looks brand new. Both the case and the instrument do not seem to be used in practice. Even the Langford sales label, in the form of a cardboard compass rose, is still glued to the circle.
The ring is marked: Gyro Azimuth circle. Serial nr. R/78/RML/224. In the lid instructions for use.

Catalog: NM. 4-16
Date: ca. 1950
HWL case: 14x29x29 cm (5.5×11.5×11.5 in)
Diam. circle: 10 in
Signed on the label: Langford, 53 Quay, Bristol
Origin: England
Condition: excellent