Compass, Magnetic Direct Reading, US Navy Mark IX Carvair It is the basic reference

It is the basic reference book for aircraft navigators in the performance of their duties

While the B-6 may have been used in some versions of dual engine aircraft such as fighters P-38 or P-61

The caging knob pulls out and turns to cage the gyro as it should

with two clamping screws

Compass, Magnetic Direct Reading, US Navy Mark IX Carvair It is the basic referenceHere is an example of the WWII era US Navy Aircraft Direct Reading Magnetic Compass Mark IX, as used in the seaplanes PBY Catalina and PBM Mariner Patrol Bombers. The compass was illuminated electrically via bulb mounted in a small compartment over the compass itself. Inside the same compartment is access to the direction compensating screws, used to calibrate the compass. This example is in reasonable condition for its age. The fluid is absent.