Greg has it exactly right. Until the introduction of LOOP2 packets about 8 or 9 years ago, the Vantage stations behaved this way. They only published pressure reduced to sea-level (SLP), so station pressure (and altimeter pressure) had to be back calculated.
-tk On Sun, Jul 17, 2022 at 7:56 AM Greg Troxel <g...@lexort.com> wrote: > > Andrea Di Saverio <disaverio.and...@gmail.com> writes: > > > If, as stated > > here > https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter, > > the `pressure` is the raw value measured by the station, why is it in > the > > `Calculations` section in the configuration file > > (https://www.weewx.com/docs/usersguide.htm#[[Calculations]])? > > I expected it cannot be calculated, rather it is the starting point to > > calculate the `altimeter` and `barometer` values. > > There is a long chain of processing. > > Somewhere in the weather station (you didn't say which one) there is a > pressure sensor, and almost always these are measuring station pressure > (with some offest that may require calibration). > > Then, various weather stations process that pressure to form barometric > pressure or altimeter pressure, because that's what ~everybody wants to > see. > > The weather station communicates some kind of pressure information to > weewx, and that depends on at least the station type, and perhaps on how > it is connected. > > weewx then does some combination of: > - use values that are reported ("hardware" is the code word for this) > - calculate values, in the case that > * they are not reported > * config, or defaults, say that's better than using the reported value > > The following behavior would not be surprising at all: > > station has station_pressure sensor > > station applies some reduction to barometric pressure > > station UI displays only barometric pressure > > station reports only barometric pressure to weewx > > weewx calculates station pressure by essentially inverting the > station's reduction to barometric, using configured elevation and > temperature > > weewx calculates altimeter pressure from station pressure and > configured elevation > > > See: > https://www.weewx.com/docs/usersguide.htm#pressure_calibration > > -- > 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 weewx-user+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/rmiilnvvldj.fsf%40s1.lexort.com > . > -- 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 weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/CAPq0zEAQFSrm1R9tCLc803r%2By3TSR_hpL39D9DAd69vV3%3DpBcA%40mail.gmail.com.
