It consists of a bakelite moulded ring 170 mm dia mounted with three sets of winding either 2, 50 & 500 turns or 2, 5 & 50 turns (depending upon the requirement) respectively with carefully insulated, connected to a heavy brass terminals.
The number of turns clearly marked between the terminals.
The high sensitive compass box (having permanent magnet) is mounted on a substantial aluminium pillar and is free to rotate upon it.
The compass is 5" in dia and has a scale graduated to single degrees.