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Hello, can you please tell me what the numbers mean on the outside ring/face of this barometer? Thanks!
Jackie C.
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The barometer is the weather instrument we use to measure air pressure. It's really quite useful. It's when the baromter rises and falls that we know if generally good or bad (cloudy or rainy) weather might be on the way.
Typically, we see units on the barometer measured in Inches of Mercury or in Hg. Pressure can be measured in a multitude of units including inches of mercury, atmosphere, torrs, hectopascals and millibars! There's even more than that! We use millibars a lot in meteorology, sometimes when you hear hurricane forecasts, the public hears that millibar term too.
Inches of mercury are good one though and the numbers are smaller and easier to read. Units in inches of mercury are generally in the 29 to 31 range. While millibars or mb are anywhere from a typical 990 mb (very low) to 1044 mb (very high). You can see why reading the units in inches of mercury might be a bit easier.
The numbers on the outside ring in the picture above are just units pressure measured in centimeters of mercury for those who like to use metric. In weather, we use the metric system frequently. When we make calculations, it is a lot less work to stay in the metric system than to convert back to the units we use in the US. Lots of equations we use have meters and centimeters in them already.
One standard atmosphere is equal to 29.92 inches of Hg or 1013.25 mb. That's a good starting point, but pressure does fluctuate below and above those numbers.
Answered by KSL Meteorologist Dina Freedman.
