It's a bit difficult to tell from the graph but I'm guessing it's altitude correction related. See https://www.weewx.com/docs/5.1/usersguide/troubleshooting/meteo/?h=pressure#the-pressure-reported-by-weewx-does-not-match-the-pressure-on-the-console and https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter for what might be going on.
Definitely make sure you have altitude set correctly for each station. Davis's calculations are in https://cdn.shopify.com/s/files/1/0515/5992/3873/files/App_Note_28_Rev_G_Derived_Variables.pdf?v=1718824378 if you want to see what those stations are doing. It's a bit of a tough read. WeatherFlow cuts to the chase with just their formula, FWIW - see https://weatherflow.github.io/Tempest/api/derived-metric-formulas.html#sea-level-pressure On Sunday, January 5, 2025 at 10:45:41 AM UTC-8 [email protected] wrote: > > First of all: compare the raw pressure readings, but therefore all sensors > have to be at the same location. > > The calculated "barometer" value depends on other measurements such as > altitude, temperature and humidity. So, if any of the other values is off, > the calculated result will be off, even when all sensors show the same > absolute pressure. > Guido Cioni schrieb am Sonntag, 5. Januar 2025 um 18:18:42 UTC+1: > >> I have 3 stations located close to each other (maximum distance is about >> 12 km). >> They all use the same hardware (Davis Vantage Vue). >> The only difference between them is that one of the stations (which is >> also the one that I'm using with WeeWx) does not have the console, so I'm >> using an external BME280 sensor to get the pressure reading. >> >> When comparing the barometer variable (which If I understand correctly >> should already be corrected with altitude and temperature) I get indeed a >> similar behaviour. >> [image: Screenshot 2025-01-05 at 18.11.45.png] >> >> However, the station with the BME280 sensor (green curve) is way off with >> respect to the other ones. >> Obviously, small discrepancies in the 'real' altitude could explain part >> of the difference, for example the one that is seen between the blue and >> red curves. However, I feel like the green line is way off possibly because >> of: >> - wrong calibration in the BME280 sensor >> - something else going wrong when computing barometer? >> >> Has anyone seen this behaviour before? Should I just use an additional >> line in StdCalibrate to correct the value of the pressure read from the >> BME280 sensor (I could use as offset the difference with the neighboring >> stations) or is there a cleaner way to correct this? >> >> Thanks >> > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/weewx-user/065cd65f-b089-4247-b69e-198488914c95n%40googlegroups.com.
