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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. | ||
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. | 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. ''Be aware of my note above, the station you choose might not correct to sea level pressure'' unless it an airport that correctly follows ICAO or WMO standards. | ||
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. You can be sure this uses sea level values. | ||
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. | 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, and airport METAR (except when reported in tenths) always rounds down, so you can be 0.9 hPa out if you use that, whereas most personal weather stations give pressure with 0.1 hPa precision. | ||
For Fine Offset clones, see [[FAQ#Cumulus_doesn.E2.80.99t_show_the_same_pressure_as_my_Fine_Offset_console]]. On a Fine Offset station, the pressure measured 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 will adjust so that is displaying the current sea-level pressure for your location. | |||
==How Accurate are PWS Barometers?== | ==How Accurate are PWS Barometers?== |
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