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#1429657 - 03/08/2017 15:11 Excel formulas
trebornicus Offline
Cloud Gazer

Registered: 30/11/2015
Posts: 20
Afternoon all,

I'm just trying to set a spreadsheet up and I'm stuck on the calculation of relative humidity. I'm using the formula at the very bottom of this page -

http://www.bom.gov.au/climate/averages/climatology/relhum/calc-rh.pdf

and have inputted it to excel as follows:

=100^(1.8096+((17.2694*B7)/(237.3+B7)))/(100^(1.8096+((17.269*B6))/(237.3+B6))).

Where B6 = dry bulb temperature, and
B7 = Dew point.

It's resulting in an irrelevant number. NOTE - the formula on the webpage has 100exp for the numerator, and the denominator just has exp[... and I think this may be where part of the problem lies, as it comes up with an error if I just enter ^[... instead of 100^[...

Can you spot any blazing errors that I've thrown in by mistake?

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#1429664 - 03/08/2017 16:43 Re: Excel formulas [Re: trebornicus]
Werner K Offline
Weather Freak

Registered: 28/11/2011
Posts: 474
Loc: Flinders Park, SA
Hi Trebornicus,

have you tried the following? :

=(1.8096+((17.2694*B7)/(237.3+B7)))/(100^(1.8096+((17.269*B6))/(237.3+B6)))*100

I think that the whole expression needs to be multiplied by 100 which would give a percentage as an answer.

I am assuming that exp(x) is equivalent to e raised to the power of x.

Cheers,

Werner

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#1429674 - 03/08/2017 17:29 Re: Excel formulas [Re: trebornicus]
trebornicus Offline
Cloud Gazer

Registered: 30/11/2015
Posts: 20
I thought you might've been onto something actually, but it spits out 9.73877E-05 whatever that means.

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#1429695 - 03/08/2017 18:49 Re: Excel formulas [Re: trebornicus]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7161
Loc: Adelaide Hills.
Originally Posted By: trebornicus
Afternoon all,

I'm just trying to set a spreadsheet up and I'm stuck on the calculation of relative humidity. I'm using the formula at the very bottom of this page -

http://www.bom.gov.au/climate/averages/climatology/relhum/calc-rh.pdf

and have inputted it to excel as follows:

=100^(1.8096+((17.2694*B7)/(237.3+B7)))/(100^(1.8096+((17.269*B6))/(237.3+B6))).

Where B6 = dry bulb temperature, and
B7 = Dew point.

It's resulting in an irrelevant number. NOTE - the formula on the webpage has 100exp for the numerator, and the denominator just has exp[... and I think this may be where part of the problem lies, as it comes up with an error if I just enter ^[... instead of 100^[...

Can you spot any blazing errors that I've thrown in by mistake?

It's:

[exp(1.096+(17.2694*Td/(237.3+Td)))/exp(1.096+(17.2694*T/(237.3+T)))]....x 100 smile .

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#1429777 - 04/08/2017 16:46 Re: Excel formulas [Re: trebornicus]
trebornicus Offline
Cloud Gazer

Registered: 30/11/2015
Posts: 20
You beauty! I knew I might've been using the wrong text somewhere in the program. Thanks very much.
I'll be back soon with another formula I'm finding myself approaching a high level of frustration with. smile

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