Aneroid barometers are usually calibrated to indicate atmospheric pressure in __________.

Correct Answer: Option A — inches of mercury and millibars

Aneroid barometers are standard meteorological instruments used to measure atmospheric pressure. To ensure compatibility with international maritime reporting standards and weather charts, these instruments are typically calibrated to display readings in both inches of mercury, common in US practice, and millibars, the standard unit for international meteorological observations.