Yes, it helps A LOT! Thank you very much, Tom. It answers to my questions. I think your explanations should be included in the wiki, in the text linked in this discussion. Questions about this or that pressure come up from time to time, and people are referred to the wiki, so these theoretical and computational basics would certainly help clarify certain ambiguities that inevitably arise. And I think that’s great, because if someone has doubts, it means they don’t treat Weewx as a black box where something goes in on one end and comes out on the other - and that’s all there is to it.
Thank you! Tomasz wtorek, 7 lipca 2026 o 23:03:42 UTC+2 Tom Keffer napisał(a): > To answer your question, it helps to look at the setup of the standard > processing pipeline: > > *StdConvert* > The first step is to convert any data coming off the hardware into the > appropriate unit system. > > *StdCalibrate* > Then user-specified corrections are made. > > *StdQC* > Set any anomalous data to None. > > *StdWXCalculate* > This is probably where the confusion lies. Given the presence of > appropriate values of temperature and altitude, StdWXCalculate can > calculate pressure from barometer, altimeter from pressure, and barometer > from pressure. Whether it does so depends on the value of the > "directive." If the directive is "hardware," it doesn't touch the value. > If it is "software" it always calculates the value, even if the hardware > emitted something. If it is "prefer_hardware" it calculates a value only > if the value is None, otherwise it doesn't touch it. > > Note that for "prefer_hardware" a new value is calculated *only* if the > old value was None. If altimeter is emitted from the dictionary > completely, it won't do anything. > > Now to answer your question, you can leave the values at their defaults: > > [StdWXCalculate] > [[Calculations]] > pressure = prefer_hardware > altimeter = prefer_hardware > barometer = prefer_hardware > > pressure: Because your driver emits a value for pressure, the directive " > prefer_hardware" tells StdWXCalculate not to touch it. > > altimeter: If the driver emits a value of None for altimeter the > directive "prefer_hardware" tells StdWXCalculate to calculate it from the > provided sensor pressure. Because StdWXCalculate appears after StdCalibrate > in the processing pipeline, it will use the corrected value of pressure. > If the driver does emit a value for altimeter, it won't touch it, which > means that you should either apply a correction to altimeter in > StdCalibrate, or use a directive of "software", forcing StdWXCalculate to > calculate it from the corrected sensor pressure. If your driver emits > nothing at all for altimeter then nothing is done. > > barometer: Same as altimeter. > > Hope this helps. > > -tk > > > > On Tue, Jul 7, 2026 at 2:11 AM 'Tomasz Lewicki' via weewx-user < > [email protected]> wrote: > >> Please help me understand the workflow for pressure/barometer >> calculations in Weewx. >> >> Here’s the situation. Let’s say my barometer reads 970 hPa. Setting aside >> how the reduced pressure is calculated, I know that it underestimates the >> pressure by 6 hPa. I’d like to inform Weewx of this without using the >> weather station console—that is, without physically entering corrections >> into the console. In other words, I want to do this in weewx.conf. >> >> I’ve made the following changes: >> [[[Units]]] >> [[[[Groups]]]] >> group_pressure = hPa >> >> [StdCalibrate] >> [[Corrections]] >> pressure = pressure + 6.0 >> >> [StdWXCalculate] >> [[Calculations]] >> barometer = WHAT SHOULD BE HERE? >> pressure = AND HERE? >> >> -- >> 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/dad98426-2004-4d3e-b1cb-6bd36d59da90n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/weewx-user/dad98426-2004-4d3e-b1cb-6bd36d59da90n%40googlegroups.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 visit https://groups.google.com/d/msgid/weewx-user/9f230829-2e34-42c1-ba65-fc72c460e32an%40googlegroups.com.
