barometer pressure readings Practice Questions

1. Standard sea-level atmospheric pressure is approximately:

• A.29.92 inches of mercury (1013.25 mb)✓
• B.30.12 inches of mercury (1019.9 mb)
• C.29.53 inches of mercury (1000.0 mb)
• D.28.35 inches of mercury (960.0 mb)

Why: Standard sea-level pressure is defined as 29.92 in Hg (1013.25 mb or hPa), which serves as the baseline reference for barometric readings in meteorology and aviation.

2. A barometric pressure reading of 1004 mb aboard your vessel most likely indicates:

• A.Slightly below normal pressure, possible unsettled weather approaching✓
• B.A strong high-pressure system with guaranteed fair weather
• C.An extreme low-pressure system requiring immediate storm preparations
• D.Normal pressure that requires no further monitoring

Why: 1004 mb is approximately 9 mb below standard pressure (1013.25 mb), indicating below-normal pressure that may signal approaching unsettled weather; further monitoring of the trend is required.

3. Which type of barometer uses a sealed, partially evacuated metallic capsule to measure atmospheric pressure?

• A.Aneroid barometer✓
• B.Mercury barometer
• C.Hypsometer
• D.Radiosonde barometer

Why: An aneroid barometer uses a flexible metallic capsule (aneroid cell) that expands and contracts with changes in atmospheric pressure; it is preferred aboard ships because it contains no liquid mercury.

4. A barograph differs from a standard barometer in that it:

• A.Records a continuous trace of pressure changes on a paper chart✓
• B.Measures pressure at higher altitudes using a radio signal
• C.Provides digital pressure readings corrected to sea level automatically
• D.Uses mercury in a U-tube to provide more accurate readings

Why: A barograph is an aneroid barometer connected to a pen-and-drum recording mechanism that traces a continuous pressure record over time, allowing mariners to assess pressure trends and tendencies at a glance.

5. When comparing readings between a mercury barometer and an aneroid barometer aboard ship, any difference is MOST likely due to:

• A.Calibration error or index error in the aneroid instrument✓
• B.The aneroid using a different unit of measurement
• C.Mercury barometers reading too high in cold weather
• D.The aneroid barometer not compensating for diurnal variation

Why: Aneroid barometers can develop index error over time due to metal fatigue in the sensing capsule; regular comparison against a mercury barometer or a certified standard and applying the resulting correction is standard practice.