Why does Weather Station Software only report up to 99% for Humidity.

[JennyLeez]

In my travels recording the high and low humidity it has become apparent that very few stations are reporting 100%. They report only up to 99%.
Looking around Cumulus I found this software gives you the ability to report 100% and a box to tick.
2 questions. Why does weather station software only report up to 99% and secondly can Weather Display be configured to report 100% as opposed to 99%.

Thanks

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[Tony]

The software is only recording what the hardware feeds it

La Crosse stations only report to 97%   

I had noticed that feature in Cumulus and thought it was a good one.

Tony

[TokWW]

My latest La Crosse hygro reports to 98% or 99% not sure which, old one was limited to 95%.  But in WD you can force it to modify the output which is in integer values, to either add an offset, and add an "add-on" gradient to lift the top range up a bit back from about 75%. 

The instruments are hard to calibrate to give the 100%, I think TT's Davis one, over accentuated the 100% for too long a period, or was that someone else's?  David's perhaps?  I don't know.  It is very hard to design a device that reads it accurately.

[David]

My Davis station usually maxes out around 98%. Occasionally I get a spike to 99% or 100% for a few seconds then it drops back again - so I think that is some sort of minor problem with the sensor.

I use the set 98% humidity as 100% in my weather software

[JennyLeez]

So in WD can you alter somewhere to make 98 or 99% report 100%

[David]

You can't set 99% as 100% it seems, but you can for 96, 97, or 98:
Control panel -> Offsets and initial rain -> Humidity offsets

[TokWW]

Yes.Control Panel and [Offsets and initial rain], but you may need the Slope adjustment feature to get 99% to 100% but it will not give 101% etc.  It crops it at 100.

[JennyLeez]

I have mine set in Cumulus as well David 100%.

Anyone reading this should make these adjustments in either cumulus or WD if they wish their station to report 100%.
Thanks you guys for input.

[beteljuice]

Two problems:

• All the usual sensors are very loose in their tolerance
• The inaccuracies are not linear

If you artificially adjust the top end, you lose the bottom end (approx. 15% - which is why most people shouldn't be trying to compute 'Burning Index') - It also means all your dew points are changed.

So be careful what you wish for 

[GrantK]

My Davis VP2 frequently reports 99% and occasionally 100% humidity.  My previous Honeywell station seldom went above 90%.

[JennyLeez]

Hi

What I have started to pick up is software also is controlling this figure as with cumulus allowing the 100% to be reported or not.

Cheers