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
On Tuesday, September 21, 2021 at 3:57:14 PM UTC-3 [email protected] wrote:
> 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 <https://en.wikipedia.org/wiki/Hygrometer>
>
> To calculate relative humidity from absolute humidity and vice versa there
> is a formula involving air temperature.
>
> WindnFog schrieb am Dienstag, 21. September 2021 um 14:29:20 UTC+2:
>
>> 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
>>
>>
>> On 2021-09-20 5:13 p.m., Karen K wrote:
>>
>> 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.
>>
>> vince schrieb am Montag, 20. September 2021 um 21:27:46 UTC+2:
>>
>>> 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
>>>
>>> On Monday, September 20, 2021 at 10:54:31 AM UTC-7 WindnFog wrote:
>>>
>>>>
>>>> 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
>>>>
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