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The entire assembly is enclosed in a sealed case that is filled with a liquid similar to kerosene. This dampens vibration and oscillation of the moving float assembly and decreases friction. 

On the front of the case, a glass face allows the numerical compass card to be referenced against a vertical lubber line. The magnetic heading of the aircraft is read by noting the graduation on which the lubber line falls. Thus, direction in any of 360° can be read off the dial as the magnetic float compass card assembly holds its alignment with magnetic north, while the aircraft changes direction. 

The liquid that fills the compass case expands and contracts as altitude changes and temperature fluctuates. A bellows 

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diaphragm expands and contracts to adjust the volume of the space inside the case so it remains full. [Figure 10-79] 

There are accuracy issues associated with using a magnetic compass. The main magnets of a compass align not only with the earth’s magnetic field, they actually align with the composite field made up of all magnetic influences around them, meaning local electromagnetic influence from metallic structures near the compass and operation of the aircraft’s electrical system. This is called magnetic deviation. It causes a magnet’s alignment with the earth’s magnetic field to be altered. Compensating screws are turned, which move small permanent magnets in the compass case to correct for this 

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