No. 1014.4 hPa is my station pressure - relative pressure. I set my elevation to (10m on Davis stations) and then set the station pressure by looking at amateur stations around me, and two official Met Office stations that I live between. This was done years ago, during a time when pressure was stable.
If you lower the elevation, down to zero for example. Station pressure drops to 1012 hPa.
OK, and do you remember the size of the correction you needed to make? I’m trying to get an idea of the raw, uncalibrated difference in station pressure between your Air module and your Davis station.
Then why does adjusting the elevation change the sea level pressure on the dashboard? It shouldn’t according to what you’ve just said - which is what I have been saying all along. Sea level pressure should be calculated from your station pressure and elevation - you should never need to adjust the sea level pressure.
Guys - threads are impossible to navigate long after the fact.
Can you start to save this kind of ‘great’ stuff someplace so all the info coming out recently telling us how stuff ‘really’ works rather than us speculating is captured someplace.
Maybe create a wiki if you want the community to lend a hand ?
Because surely as, by definition, SLP depends on elevation, changing elevation changes the SLP? The point of course is that you shouldn’t have to fudge the elevation to get the correct SLP, which @WFmarketing discussed above.
Stop and look at what you just said… SLA IS Calculated from station data, adjusted by height. The absolute is STATION data, and yours is wrong. When WF roll out the CL for pressure, yours will be corrected and all would be good.
Point I raised some weeks back, even for me as moderator, I remember I saw a reply but hell where was it …
I have started a local litlle database with things as the forum isn’t handy for wiki style info. I hope WF will do this once they have some more time spare …
dare I suggest one of the field testers set up an unauthorized (so to speak) wiki for the interim ?
setting one up and populating it takes time. If it is as a temp solution … maybe a pity except if the WF staff decides to use the same script, hence database move … but again, better know before and not too late
Here is the formula used for calculating Sea Level Pressure: https://weatherflow.github.io/SmartWeather/api/derived-metric-formulas.html#sea-level-pressure
Relax and smile everyone.
I feel as though i’m not getting my point across. I have tried my very best, but it seems not to be working.
I just want to add, i’m not the only one who thinks this is wrong. On another weather forum, users with other weather stations agree with me.
Here’s some other points I want to raise.
I keep reading about how the weather data is supposed to be ‘user friendly’ and kept ‘simple’ for those that might not be savvy when it comes to this sort of thing. But, in all honesty (owning stations for over ten years) some of the options and output on the dashboard are the most complicated I have ever seen in a weather station.
If there’s going to be a problem with the barometric side of things, then you should include an option to show either station pressure, or SLP, on the main dashboard page. If my station get’s calibrated correctly, by that I mean; I can put in my correct elevation and get the right station pressure, then I have no choice in having sea level pressure showing on my dashboard page which will look wrong when comparing it to my Davis and surrounding stations.
I’ll support WF all the way, as I really do like this station. But, as I touched upon above, I find some things completely and utterly baffling about it - some of it is straight forward, but the pressure side of things is completely bonkers. What you may think of as intuitive is actually over-complicated.
One thing I have learned in the tech business over the years is to give people options. on/off - stop/go etc. It makes life far easier.
I’m going to stop posting for a while. So, best regards and enjoy mother nature!
Maybe, just maybe…
The reason that the reading is wrong is because …
wait for it…
The Air is defective.
I said Maybe.
Don’t fret @moeythomas . Seems to be simply a matter communication. It also seems that WE ACTUALLY AGREE on everything you note here. For example:
We agree, and this is how the system works.
This is a good idea. We’ll certainly consider it !
We love your feedback and your passion and we’re listening. All good.
tina is a reliable and a good source of spotting the anomalies she has never been wrong in all the time i have known her and she is the ideal bug tester …i can speak from experience so trust her views she would be the ideal,field tester because she has a vast experience that you would benefit from immensely…
The Fudge Factor I employed puts my Air at -.2 mb average error according to CWOP’s Q.C. analysis, I must have done something right. Meanwhile back in the lab using a NIST traceable barometer or absolute pressure gauge would be the preferred method. So the Fudge Factor I use will do until WF includes calibration routines that compare official surrounding WX stations and Airports (and commercial airports require accurate barometrics to give proper altimetry data), then AutoMagically apply the corrections.
So i put my elevation back to 0.7 m below sea level.
I adjusted to -20 meter to get the right pressure as on the KNMI stations.
If I understand it… When the CL is deployed it should show a better pressure?
It’s 2-3 mb to high now.
Exactly! When the CL is deployed it’ll produce a much better station pressure, which when combine with your elevation of 0.7 m below sea level, should match the sea level pressure of the KNMI stations.
You adjusted what to -20 meters?
Thanks, @moeythomas - we totally agree - reporting air pressure values can be confusing! But we’re pretty confident that we’re doing it correctly, and I think we actually completely agree with what you and others are saying in this thread. Hopefully this post will clear up the confusion. First, some definitions:
Sea Level Pressure = Barometric Pressure = Relative Pressure = air pressure, adjusted to sea level
Station Pressure = Atmospheric Pressure = Absolute Pressure = air pressure, measured by the sensor
There are two pressure values reported in the Smart Weather app. One of them is called “station pressure” - it’s also called “absolute pressure” or “atmospheric pressure”. This is the value actually measured by the sensor. This value is not of much use to people, unless for some reason you want to know what the actual pressure is at your house (maybe for brewing beer or baking bread?).
The other pressure value reported is “sea level pressure” - it’s also called “relative pressure” or “barometric pressure”. This value is NOT what the sensor actually measures. Rather, it’s the value that would be measured if you were standing at sea level under the same sort of atmospheric conditions. It’s adjusted or “normalized” based on the sensor’s total height above sea level. In the Smart Weather context, the “total height” is the sum of the “elevation” value that you set for your station and the “height of the ground” value that you set for your AIR device.
The value displayed in the main interface of the Smart Weather apps is sea level pressure. Why? Because that’s the most common way to report pressure and it’s the only way to facilitate comparison between locations with different altitudes. This let’s you compare apples to apples. This is the value meteologists care about. This is the value most weather services, websites and apps commonly report. This is also the value that the Davis console displays, as do most other home weather stations. It’s also the value an analog mercury barometer should show.
Aha! This may be part of the confusion! These two values you mention - “sea level pressure” and “relative pressure” - are the same thing!! The other value, “station pressure” (aka “absolute pressure”), is the one that’s no good to you! We should probably just take station pressure out of the app (except then we’d have a few bread bakers and beer makers demand we put it back in)!
This is definitely another source of the confusion. Yes, adjusting your elevation above sea level is a crude but effective way to “calibrate” a presure sensor. Some weather stations even advise you to do this. But it is not normally necessary with your AIR. You should simply set the elevation of your station and height above ground of your AIR to the actual values where it’s located, and then (assuming your AIR’s pressure sensor is calibrated) your “sea level pressure” (aka “relative pressure”) will be correct.
That said, we have learned recently that many AIR units from the latest production batch (the ones that were shipped over the past few weeks) seem to be out of calibration, often reporting 2-4 mbar too high. The calibration process at the factory, normally very good for the pressure sensor, failed for some reason.
As a result, we have bumped up the priority of adding the pressure component to our Continuous Learning system. As noted above, we expect that to happen in the next week or two.
If you can’t wait for that, and you’re pretty sure what your pressure sensor should be reading, feel free to contact support@weatherflow.com and they can perform a manual calibration for you.
Yes, we do try to save good stuff like this! We’ve just updated the Smart Weather FAQ with some of this “how to read pressure” info.
Yes! If you believe your pressure sensor is out of calibration, please resist the urge to change the elevation in order to “fix” it. When we roll out the pressure component of the CL system (which will be very soon), your pressure value will get better.
Thank you!! Please, everyone, keep the feeback coming. We still have some kinks to work out and we can’t do it without you. Your input critical to improving the whole smart weather station ecosystem!
We truly hope this latest post helps clear up the confusion. But please let us know if any remains!
PS: Although this is post is “owned” by @dsj, much of the info came from several people much smarter than he.
PPS: If you happen to have your AIR mounted at sea level, your station pressure will match your sea level pressure and you could have ignored this thread completely! 
In case it hasn’t been posted recently, this weewx document describes the three different types of pressure readings:
https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter