Which component of the VSI experiences a decrease in pressure during a climb?

The vertical speed indicator (VSI) uses a diaphragm as a key component to measure changes in atmospheric pressure related to the aircraft's vertical movement. When an aircraft climbs, the ambient pressure surrounding the VSI decreases due to the higher altitude. The diaphragm inside the VSI expands or contracts based on the difference in pressure between the inside of the diaphragm and the outside atmospheric pressure.

During a climb, the static port, which is responsible for sensing the outside ambient air pressure, detects the decreasing pressure as the altitude increases. This causes the air inside the diaphragm to have lower pressure than before, allowing the diaphragm to move in response. The movement of the diaphragm then translates to the VSI needle indicating a climb rate.

The other options do not directly experience a decrease in pressure during a climb. The static port provides the pressure readings, the aneroid wafers are part of altitude measurement systems but do not signify pressure changes for vertical speed directly, and the pitot tube measures dynamic pressure, which is relevant for airspeed but not for the VSI. Therefore, the diaphragm is the correct answer as it directly reacts to the pressure changes resulting from the aircraft's vertical ascent.