Relative humidity query

[WindnFog]

I have read the documentation for the Davis Vantage Vue console, weewx, and searched the message board.  If the answer is there, I can't find it.  Is the humidity that we get relative humidity or just humidity?  I know the difference, but I can't seem to find which weewx reports.

- Paul VE1DX

[vince]

https://www.weathershack.com/products/davis/manuals/6351-manual.pdf says relative is what's displayed on the console (see page 20) with another mention on page 44

[Karen K]

Relative humidity is in percent. Absolute humidity is in gram per cubic meter. So you see by the unit what kind of humidity reading it is. "Just humidity" does not really exist.

[Paul Dunphy]

     Thanks to Vince and Karen. I should have clued in on the % sign on my Davis Console. I interpret this as relative humidity, at least on a Davis setup. That brings me to the reason for the question. Should I be reporting the results on my website graphs and tables as "Relative Humidity," and if so, is this something that's standard across all weather stations (i.e., a weewx change), or is it an "It depends on your hardware?"
- Paul VE1DX

--
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/wZ3thjZZ-9g/unsubscribe.
To unsubscribe from this group and all its topics, send an email to weewx-user+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/cd55fc87-6e67-4258-8998-71a90671f38fn%40googlegroups.com.

[Karen K]

How many water the air can contain depends heavily on air temperature. If the air is cold, it is only a small amount. If the air is hot, it is a lot. So how can you express the humidity in a reasonable way? The standard way is to compare the amount of water in the air to the maximum possible at that temperature. That is relative humidity, and it is expressed in percent. 

If you have got an old fashioned hygrometer (containing a hair for measurement), it shows the humidity in percent, too.

Wikipedia: Hygrometer

To calculate relative humidity from absolute humidity and vice versa there is a formula involving air temperature.

[WindnFog]

   Got it!  From page 44 of the manual, as Vince points out, "Relative humidity, therefore, is not actually a measure of the amount of water vapor in the air, but a ratio of the air's water vapor content to its capacity. When we use the term humidity in the manual and on the screen, we mean relative humidity."

    So weewx uses whatever the Davis weather station (or any other supported weather station) provides and does no further calculations because it's already converted to relative humidity by the hardware.

- Paul VE1DX