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→Sea level pressure
The pressure is returned in Pascals (an unit from [https://en.wikipedia.org/wiki/International_System_of_Units International System of Units]). 100 Pascals = 1 hPa = 1 millibar. The barometric pressure is often using the millibar or mm of mercury as unit. Just note that 1 pascal = 0.00750062 mm of mercury mercure.
The pressure is returned in Pascals (an unit from [https://en.wikipedia.org/wiki/International_System_of_Units International System of Units]). 100 Pascals = 1 hPa = 1 millibar. The barometric pressure is often using the millibar or mm of mercury as unit. Just note that 1 pascal = 0.00750062 mm of mercury mercure.
=== Sea level pressure ===
=== SLP: Sea Level Pressure ===
You can also calculate the altitude from the pressure. However, to proprely measure the altitude, you need to know the pressure at the sea level (hPa, pressure that change every day)!. The BMP280 is really precise, however it may be difficult to have precise evaluation of the altitude if you don't know the pressure at the sea level (the pressure {{underline|of day}} at the sea level).
You can also calculate the altitude from the pressure. However, to proprely measure the altitude, you need to know the pressure at the sea level (hPa, pressure that change every day)!. The BMP280 is really precise, however it may be difficult to have precise evaluation of the altitude if you don't know the pressure at the sea level (the pressure {{underline|of day}} at the sea level).
=== Pressure, SLP and altitude ===
SLP means Sea Level Pressure (also knwon as PNM pressure). Most of the advanced the meteo station does transform the current pressure to SLP pressure before displaying it. If all pressure in the country are expressed as SLP pressure then it is more easy to determine the wind (and cloud) movements across the country, from higher pressure to lower pressure.
Here is a small picture that shows the relation between SLP pressure, altitude and pressure given by a sensor (like the BMP280).
[[Fichier:ENG-CANSAT-BMP280-50.jpg]]
{{ENG-CANSAT-TRAILER}}
{{ENG-CANSAT-TRAILER}}