Compass, Vertical, Direct Reading Magnetic, Type B-20
This WWII-era Direct Reading Magnetic Compass Mark X, Kollsman FSSC number 88-C-855 was made for aircraft of the US Navy.
The interesting aspect of the design of this compass is that the directional mechanism lies horizontally within the rear chamber, and displays the direction on a vertically-mounted compass card. In addition, the desired course heading can be selected by rotating the knob at the bottom center of the dial, which turns the double-arrow pointer clockwise or counter-clockwise. The single pointer would indicate true magnetic north. There are adjustment screws for E-W and N-S for calibration alongside the course setting knob.
This example is in good cosmetic condition but does not function. The fluid in the rear chamber is absent, the single pointer no longer rotates, and there is a slight internal rattle.