In level flight, the pressure inside the capsule and the case will be the same, so the pointer will remain in its horizontal position, indicating a zero rate of climb.
B.
If the aircraft climbs, the static pressure in the capsule will decrease at a quicker rate and the capsule will collapse slightly, and will cause the pointer to indicate a rate of climb.
C.
When the attitude of aircraft become level flight from climbing, the inside pressure will outflow, and the pointer turns to zero.