Which units are used for the Altimeter Setting pressure parameter?

The correct choice for the Altimeter Setting pressure parameter is inches of mercury. This unit is commonly used in aviation to report altimeter settings, particularly in the United States. The altimeter setting is crucial for pilots as it ensures that they are flying at the correct altitude based on pressure changes in the atmosphere, which can affect how high or low an aircraft actually is compared to sea level.

Inches of mercury is a traditional unit that dates back to the early days of barometry and aviation. It provides a familiar reference for pilots, as altimeters calibrated in inches of mercury can give pilots and air traffic controllers consistent readings regardless of local weather conditions, allowing for safe navigation and altitude maintenance.

Other units like millibars and hectopascals are indeed used in meteorology, especially in weather reporting and studying atmospheric pressure, but they are not typically used for altimeter settings in aviation practice. Centimeters of mercury, while also a valid measurement of pressure, is not standard in aviation for altimeter settings. Thus, inches of mercury remain the preferred and mandated unit in the context of altimeter settings utilized in aviation.