What position should the air damper valves be in when checking gas pressure during a climb?

When checking gas pressure during a climb, the air damper valves should be closed. This is because closing the air damper valves helps ensure that you are measuring the gas pressure under conditions that accurately reflect the performance of the system without interference from surrounding air. In a climbing scenario, the pressure might fluctuate due to changes in altitude, which can impact how the gas performs if the valves are open. By keeping the damper valves closed, you can obtain a precise and consistent reading of the gas pressure that is necessary for proper monitoring and adjustments during the climb.

The other responses suggest varying degrees of openness for the air damper valves, which could lead to inaccurate readings and undermine the effectiveness of the testing process. A fully open or partially open position could allow for outside air to influence the pressure readings, while "invariable" does not specify a useful or practical setting for the valves. Therefore, closing the damper valves is crucial for maintaining the integrity of the pressure measurements during climbing operations.