Modifications

If you want to obtain an accurate altitude value with the BMP280 then you need to know the pressure at the sea level (''the baseline'') with precision.  

If you want to obtain an accurate altitude value with the BMP280 then you need to know the pressure at the sea level (''the baseline'') with precision.  

Once the baseline value corrected, you will have the correct altitude:

Once the baseline value corrected, you will have the correct altitude.

 

 

The sensor would return the right altitude (104m) for the sensor which is quite good since we are not in the tower (like the reference weather station).

=== The pressure is not correct atmosphérique semble incorrecte! ===

=== The pressure is not correct atmosphérique semble incorrecte! ===