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Pressure Measurement: Difference between revisions
Pressure Measurement (view source)
Revision as of 07:04, 15 September 2013
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==Setting the Datum== | ==Setting the Datum== | ||
All weather stations allow you to adjust the pressure for sea level. You should not make the adjustment within Cumulus. | All weather stations allow you to adjust the pressure for sea level. You should not make the adjustment within Cumulus. | ||
For Fine Offset see [[FAQ#Cumulus_doesn.E2.80.99t_show_the_same_pressure_as_my_Fine_Offset_console]]. | For Fine Offset see [[FAQ#Cumulus_doesn.E2.80.99t_show_the_same_pressure_as_my_Fine_Offset_console]]. On a Fine Offset station, the pressure measure at the station is called Absolute Pressure, and the pressure corrected to sea level is called Relative Pressure, and the console displays the characters "rel" when it is displaying Relative Pressure. It is therefore the Relative Pressure reading which you need to adjust so that is displaying the current sea-level pressure for your location. | ||
The best way to get MSL pressure at your location is to go to a site like [http://www.wunderground.com/ Weather Underground] and enter your location. It will find a weather station nearby and give you the current MSL pressure. It's a good idea to choose an airport site because you can be sure that it has been accurately reduced to MSL pressure. | The best way to get MSL (sea level) pressure at your location is to go to a site like [http://www.wunderground.com/ Weather Underground] and enter your location. It will find a weather station nearby and give you the current MSL pressure. It's a good idea to choose an airport site because you can be sure that it has been accurately reduced to MSL pressure. | ||
Alternatively, look at a isobar chart at a site like [http://www.meteorologica.info/UKisobars.htm weather superstore], and interpolate for your location. | Alternatively, look at a isobar chart at a site like [http://www.meteorologica.info/UKisobars.htm weather superstore], and interpolate for your location. | ||
The best time to set your datum is when the pressure is not changing either with time or between nearby locations. Note most sites only give pressure to the nearest hPa, so you can be 0.5 hPa out if you use that, whereas most personal weather stations give pressure with 0.1 hPa precision. | The best time to set your datum is when the pressure is not changing either with time or between nearby locations. Note most sites only give pressure to the nearest hPa, so you can be 0.5 hPa out if you use that, whereas most personal weather stations give pressure with 0.1 hPa precision. | ||
==How Accurate are PWS Barometers?== | ==How Accurate are PWS Barometers?== | ||