🔍 Key Concepts

• Relationship between air pressure and weather systems on surface weather maps • Common meteorological units: what is measured in degrees, what is measured in percent, and what is measured in inches or millimeters of rain/snow • How barometers are used on ships and what quantity a barometer actually measures

💭 Think About

• Think about which of the four options you would normally see displayed on or associated with a barometer on a vessel • Consider how mariners use millibars when tracking storms or low/high systems on weather charts—what quantity are they comparing? • Ask yourself: if the value in millibars is falling rapidly, what kind of weather change is usually expected, and which of the four choices that relates to?

✅ Before You Answer

• Match each choice with its usual units: humidity (what unit?), temperature (what unit?), precipitation (what unit?), pressure (what unit?) • Recall that standard atmospheric conditions at sea level are often given as about 1013 in this unit—what physical quantity is that number describing? • Verify which of the four options is directly connected to reading and interpreting a barometer on board ship