What is the typical frequency for comparing two aneroid instruments used to determine altimeter settings?

The typical frequency for comparing two aneroid instruments is each time the altimeter setting is determined. This practice is crucial for ensuring accuracy in altitude measurements, which can significantly impact flight safety. The altimeter setting is vital for pilots because it provides them with the necessary information to maintain the correct altitude during flight, helping to prevent incidents such as controlled flight into terrain.

By comparing the readings of two aneroid instruments at each altimeter setting determination, any discrepancies can be identified and addressed immediately. This not only helps in maintaining the precision of the instruments but also ensures that they remain reliable over time. Regular comparisons serve as a form of calibration, reinforcing the integrity of the data received by pilots and air traffic control.

In contrast, longer intervals like weekly or monthly checks would not be sufficient for the dynamic and highly variable conditions encountered in aviation. Regular adjustments and validations of altimeter settings are essential for safety and performance in the aviation environment.