If you are comparing your external sensors to your console's barometer keep in mind that the offset does not mean the sensor is out-of-spec. An absolute offset is not a specification. It is just the sensor correction offset so that all your barometers read the same absolute pressure. I am assuming you using the console as your reference and you have calibrated it with a close-by airport using METAR or mesowest readings or equivalent.
To answer your question if QNH = Altimeter? Altimeter includes a landing gear offset of 10 feet = 0.3mb/.01 inHg. I believe that QNH does not have that peculiar offset. Although most sources equate the two, I think the equations are different. Lastly you were asking about different definitions of SLP? It is easy to get confused here because it is confusing. I know of at least 6 different equations for Altimeter and there might be dozens of different country-specific equations for (M)SLP. To make things more interesting both Altimeter and (M)SLP can be referred to as "SLP".as both are reduced to sea level elevation. As you are aware, if you hook up your console to WeeWX, WeeWX will automatically calculate Altimeter and (M)SLP using the proper algorithms. Need to adjust the current algorithm for your region? You can modify it. On Thursday, June 2, 2022 at 1:52:52 PM UTC-4 Greg Troxel wrote: > > thanks for the comments. I will be digesting all of the replies and > CWOP data and coming up with a cal plan. > > "[email protected]" <[email protected]> writes: > > > For a Davis VP2, SLP is already calculated for you in the console so all > > you need is the elevation of your sensor. Hwever you still need to check > if > > your barometric sensor is accurate or not, > > Agreed. > > > The BMP280, BME680 are accurate > > to 1 hPa and so is the VP2 barometric sensor. The newer Bosch barometric > > sensor (BMP390) is accrate to 0.5 hPa. > > My data so far indicates that a BME280 and a BME680. > BME680 is +2.4 hPa from VP2. > BME280 is +1.4 hPa from VP2 > Brunton ADC is -0.1 hPa from VP2. > > So I don't believe those claimed accuracies. I am tentatively > believing that VP2 and Brunton ADC are correct until I can take the ADC > to visit other barometers. > > > You could calibrate your VP2 with the higher spec BMP390. Just match the > > pressures and you are done! or alternatively you can match Altimeter > with a > > close-by METAR. > > I am going to try to compare my barometric and altimeter pressures with > NWS stations on a day with a low rate of change. > > > So no, we will not be achieving 0.05 to .10 hPa accuracy WMO standards > with > > our consumer grade personal weather stations! > > VP2 seems pretty stable so I think 0.2 hPa is not crazy. > > > Keep in mind that different countries use different pressures. Most > > countries don't use SLP or Altimeter - they use QNH in whole integer > > amounts which makes matching difficult as you would have to match 1013, > > 1014, 1015, etc. If you luck out, some countries publish decimal QNH > like > > the BOM in Australia. > > I thought QNH was Altimeter. The US uses that in aviation and SLP or > barometric pressure for weather. But yes, roudning to whole hPa makes > it hard. > -- 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 on the web visit https://groups.google.com/d/msgid/weewx-user/8f118f1a-f5f7-46c5-aa83-d41c53493e02n%40googlegroups.com.
