Paul, I disagree. Simply adding a constant offset to Absolute does not give you Altimeter. I understand your point in that Altimeter is a similar thing that uses a temperature constant, but Altimeter should be something that is properly calculated from Absolute using a proper formula. I'm sure that WeeWX already has a built in conversion to get from Absolute to Altimeter.
The only online weather service that requires Altimeter sent to them that I know of is CWOP. Yes there are some people that prefer to only use Altimeter and for those people there are other means to accomplish this and that would be to zero out their elevation on their consoles. Yes the Relative Pressure out these stations is not technically totally accurate Sea Level Pressure but perhaps that is why they call it Relative pressure and they don't try to pass it up as Sea Level Pressure. The Relative Pressure Offset is an average offset. If you were to calibrate to the exact offset for a given pressure amount you would notice that when the pressure changes that your Relative would no long match as well the Sea Level Of that you calibrated against. That is why when you figure out your Relative Offset you should be using 1013.25 hPa as your Sea Level Pressure. You can read a great deal about how to best calibrate these a Fine Offset stations on wxforum.net. On Wed, Jul 29, 2020, 8:50 PM Paul R Anderson <[email protected]> wrote: > Should we map 'altimeter': 'relbarometer' ? > > Gw1000 produces 2 pressure readings: > As defined by Ecowitt Calibration of barometric pressure settings > <http://www.ecowitt.com/news/102.html> > *Absolute Pressure* > "Absolute barometric pressure, can be calibrated at manufacturing time by > comparing with a precise instrument that measures pressure at the same > location. In practice, sometimes small adjustments of a few hPa may be > needed" > *Relative Pressure* > "The relative pressure represents what the air pressure would indicate if > your station was at sea level and depends on the altitude of your console > and cannot be known in advance. This is why it needs an adjustment" > > If you work your way thru there cal procedure you will see that you use > the WS View app to set 2 offsets: > Abs Offset > Rel Offset > To set Rel Offset they have you determine station elevation and direct you > to a site that produces a offset based solely on elevation. So *Rel > Offset* is a *STATIC *offset applied against your Absolute Pressure. It > never changes if we set a Rel Offset of 6.0 hPa then Relative Pressure will > always read 6.0 hPa higher than Absolute Pressure. > As we see in WeeWX Wiki > > Station or Gauge Pressure (key *pressure*): This is the absolute, raw > pressure as measured by your instrument. It is not corrected for altitude > or pressure. Pilots call this QFE > Sea-level Pressure (*barometer*): This is the pressure corrected for > altitude, temperature, and (frequently) humidity. Pilots call this QFF. > This is the value displayed by the standard skin. > Altimeter Pressure (*altimeter*) : This is the pressure corrected for > altitude, using a standard temperature profile. Pilots call this QNH. > > Because we are on a very limited device which does not attempt in any way > to apply a temperature compensation I believe that mapping 'altimeter': > 'relbarometer' may be more appropriate. StdWXCalculate will calculate > barometer for us when it appears in a template. > Thanks > Paul > > >> >> 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/F82E7D44-2090-4C09-9BA6-8355FE73841F%40gmail.com >> . >> > -- > You received this message because you are subscribed to a topic in the > Google Groups "weewx-user" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/weewx-user/3KF7XMLQGsA/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/CAOAVAefsj387Cx%2B8ffLt%2BjLS3vhnrwGp2%2Bpy3zUeuc2h7etKDg%40mail.gmail.com > <https://groups.google.com/d/msgid/weewx-user/CAOAVAefsj387Cx%2B8ffLt%2BjLS3vhnrwGp2%2Bpy3zUeuc2h7etKDg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- 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/CAG91bKzfswzZ-FDZQfAG%3DJbMoDx2YW%3DzpRi7FVHDycFuP2neOg%40mail.gmail.com.
