Pardon me for jumping in here; but I've done a lot of fiddling and research on just this topic.
Some background, I currently have THREE pressure sensors within a 600' radius, and Acurite 5-n-1, the pressure sensor that comes with an "original" PurpleAire Outdoor unit and the sensor in my Tempest WeatherFlow. At one time or another I've had as many as five pressure sensors. Being in the US, I typically display pressure as inHg; but when fiddling, I use millibars. Right now, my Tempest WeatherFlow is reporting 29.736 inHG, my purpleair is reporting 29.08 inHG and the Accurite is reporting 29.63 inHG. I've NEVER seen agreement on any 2 sensors, let alone 3 or 4 and I've seen differences as much as .5 inHG I'm 3 miles and about 100 feet lower than S40 (our nearest airport) which is reporting 29.81. But I'm also reporting a CORRECTED (to a NIST traceable sling psychrometer) temp of 94.2 as opposed to 86 at S40. For what it's worth, the purpleaire is reporting a temp of 104, because the sensors are inside a small non-ventilated case. I also participate in the NOAA Citizen's Weather Observer Program, and here's what they say over the last 30 days. Average barometer error: 0.1 milliBars Error standard deviation: 0.4 milliBars When I first started w/CWOP, I went crazy trying to correct stuff and actually did correct my Acurite to SLP; but Based on the current CWOP data, which is taken from the Tempest, when I installed that 3 years ago and observed the differences daily for a month, I gave up trying to "calibrate" it. I do check once or twice/week and have never seen anything but two "thumbs up" out of CWOP except during frontal passes. It's also been my experience that even 3 miles and 100 ft can make a large difference, a few tenths inHG, especially when you consider temperature as well. Bottom line: 1) With "consumer grade" equipment, you're never gonna get NIST reliabilty or traceabilty 2) Different sensors will report different results. Pick one, get it to approximate either Sea Level Pressure or "altitude corrected" pressure and then observe it for a while. And as far as what WeeWx does, "What Tom and the documentation say". On Tuesday, July 7, 2026 at 2:11:16 AM UTC-7 Tomasz Lewicki 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/1fcc87ca-6e24-48f5-bf3a-358fc983c915n%40googlegroups.com.
