Barometers may be graduated in either inches of mercury or which other measurement?

Barometers, which measure atmospheric pressure, can be graduated in various units. In addition to inches of mercury, they are commonly graduated in millibars (or hPa, hektopascals). This unit is part of the metric system and is widely used in meteorology because it provides a more convenient scale for expressing atmospheric pressure, especially given its relationship to other metric measurements.

In meteorological contexts, a millibar is defined as one-thousandth of a bar, with the standard atmospheric pressure at sea level being approximately 1013.25 millibars. The use of millibars allows for clear communication of weather-related pressure changes and is standard practice in weather reports and forecasts.

While other units such as pascals, atmospheres, and kilopascals can also be used to measure pressure, for barometers, the millibar is the most practical and conventional alternative to inches of mercury, making it a preferred choice in many settings.