Dear Tom,
I recently inherited an old German barometer with a scale of numbers from 70 to 79. How can I convert the readings to our local pressure?
Werner Lang
Dear Werner,
Your barometer was produced with a metric scale that gives the barometric pressure reading in centimeters of mercury instead of the inches of mercury commonly used in the United States.
To convert the centimeter pressure readings to inches, divide by 2.54 (the number of centimeters in one inch). For example, if your barometer was reading 76 cm, that would equate to 29.92″. In winter during one of Chicago’s subzero spells when a large arctic high pressure center covers this area, your barometer might read as high as 78 cm (30.70″). On the other hand, during the passage of an intense low pressure system, the barometer reading could drop as low as 73.4 cm (28.90″).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
