Naval Course Corrector, Mounted for Display
This large shiny metal device is a WWII-era naval Course Corrector, used to convert, mechanically, a ship's True Course to Magnetic Course and to Compass Course when variation, deviation, or compass error is known.
Two inner dials labeled Magnetic Course or Bearing and Compass Course or Bearing rotate within the outer ring labeled True Course or Bearing. A mechanical arm rotates around the axis with locking screws to capture its position on the two inner dials.
It is a heavy instrument and is mounted on a wood-framed base for display. The instrument is 13 inches diameter and the frame is 18 inches square.