The purpose of the counter pointer pressure altimeter (Figure 6-8) is to show aircraft height. By studying the dial of the indicator, you can easily understand the procedure for determining the height of the aircraft. A description of the mechanical operation of this altimeter follows.
Atmospheric changes cause movement of the two aneroid diaphragm assemblies. These assemblies move two similar rocking shaft assemblies mutually engaged with the main pinion assembly. This movement goes to the handstaff assembly, which operates the hand assembly and drives the counter mechanism through a disk. Because of the special design of the hand assembly, the counter indication is never obscured. An internal vibrator minimizes friction during the instrument’s operation.
You make barometric corrections by turning the externally located knob. The knob engages the barometric dial and the main plate assembly that supports the entire mechanism. You make adjustments so the reading on the barometric dial corresponds to the area barometric conditions in which the aircraft is flying.
