Identification

• Barometric pressure, which decreases with altitude, is reported by the National Weather Service. It is measured as inches of mercury at the surface, and in millibars, or hectopascals, aloft.
  
  

Geography

• Below 2,000 to 3,000 feet, air pressure drops 1 inch of mercury for every 1,000 foot gain in altitude, while altimeters are corrected by 1 millibar for each 8-meter gain in altitude.
  
  

Measurements

• The average air pressure at sea level is 29.92 inches of mercury, and 1013 hectopascals, and at 3,000 feet drops to 26.82 inches/700 hectopascals. On an airplane at 35,000 feet, it is a low 7.04/5.6 respectively.
  
  

Research

• Measurement values on the standard atmosphere table are based on mathematical formulas, which have been found to be close to balloon and airplane measurements at different altitudes.
  
  

Effects

• Many people experience discomfort or pain in their ears when traveling on a fast elevator or on an aircraft. This is because of the effect of rapid air pressure changes on the human body.