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Calibrating a Barometer

MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Calibrating a Barometer

Last week I bought a second hand barometer. Many years ago an ex neighbour told me that they need to be calibrated.
I went on the web to try and find out how this should be done. The instructions were to find the sea level were I live and it must be set when the weather is fine.
Apparently  the sea level varies slightly  depending on what part of the village I live in , but on average it is about 29 about sea level . Perhaps I am a bit dim, but the instructions didn't seem that clear . Would I be right in assuming  that as the level in the village is approx. 29 above sea level , that I should set the needle at 29 when the weather is fine ?
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Registered: 04-08-2009

Re: Calibrating a Barometer

You need to either set it at your actual height ABOVE sea level, or better still, select the actual air pressure at the time you set it. You can get that by selecting your location from here..
http://www.wunderground.com/
Enter where you are in the search box, then after that page has opened select "Full Forecast" and look to see exactly where the weather stations are nearest to you. Select the closest and you should also find the air pressure shown. Most weather stations report every ten seconds!
MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Re: Calibrating a Barometer

Many thanks I will have a look at that.
MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Re: Calibrating a Barometer

Perhaps my barometer is not a very good one . It just seems to show sections ranging from 31- 26. I cannot see any reference to air pressure.
I visited the website you suggested . It came up with a weather station showing the next village. It showed the present air pressure there as 993.79 hpa
Community Veteran
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Registered: 04-08-2009

Re: Calibrating a Barometer

Does the dial show any units, such as Inches Hg (inches of mercury). Those numbers look like inches of mercury to me, although the 26 is a bit low.
Enter the hPa reading into this 
http://www.convertunits.com/from/hpa/to/inhg
Your current hPa reading is about 29.3 inches of mercury.
MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Re: Calibrating a Barometer

Yes the conversion does say 29.34 to 2 decimal places.
Apologise for my ignorance but the dial just shows these numbers within a diamond  30 at the top of the dial and 27 at the bottom of the dial with what appears to   be 20 sections in between for eg
From 29 leading upto the top(30)  halfway between these lines it's marked  29.5 but no reference to inches
Sorry to be a pain

P.s It looks as if the setting is quite a way  out for this village at the moment . The needle is  presently  showing approx 30.4
Community Veteran
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Registered: 15-06-2007

Re: Calibrating a Barometer

that is because it would have been understood given the age of the barometer
Community Veteran
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Registered: 04-08-2009

Re: Calibrating a Barometer

Those are inches. Just set it to a guesstimated 29.3 on the dial.
Given the age of the barometer there might not be enough adjustment available, but set it to the nearest.
MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Re: Calibrating a Barometer

Will do, many thanks for all your help
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Registered: 06-11-2007

Re: Calibrating a Barometer

I think the barometer should be mounted on the inside, of an outside wall.... and it should be left alone for a few days to " settle in".. to it`s new environment before doing the resetting via the screw adjuster on the back...
If you want to keep a record of the ups and downs of life, you may like to make up your own "graph paper"...  by using this...

http://www.worksheetworks.com/miscellanea/graph-paper/standard.html
you can set the size of the squares ( and therefore the number on each sheet) by the settings at the bottom of the screen....  BUT.. a bit further down, you need to alter it from US size to A4 for uk printing...
Trial and error is the only real way, although you do get a visual "on screen" before you actually print out,  so , in theory, you should be able to count across for the 30 days  (you can add the final 31st day by pencil when needed)..
MightyMouse
Grafter
Posts: 226
Registered: 17-12-2007

Re: Calibrating a Barometer

Thanks Shutter, I was going to mount it on the wall this morning, then a cup of tea and Bargain Hunt seemed to become more urgent .
Having since had a look at some of the Barometers on line, I will see how this one goes and probably invest in a new one at a later date.  

P.s I have since found this information online :-  Q6 Should a barometer hang on an outside wall? [top]
It makes no difference to the pressure reading which wall you hang a barometer on. There may be a slight difference in temperature but not pressure. The pressure is the same inside as well as outside.
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Re: Calibrating a Barometer

You've now got me checking and adjusting my mechanical Barometer Roll eyes
Fortunately I have a semi-pro weather station with an accurate Barometer.
My old mechanical Barometer was only slightly out Smiley
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Re: Calibrating a Barometer

That's probably why you shouldn't use an analogue barometer on a house landing. You might have a crash if it is wrongly calibrated.
Now Zen, but a +Net residue.
itsme
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Re: Calibrating a Barometer

Quote from: MightyMouse
It makes no difference to the pressure reading which wall you hang a barometer on. There may be a slight difference in temperature but not pressure. The pressure is the same inside as well as outside.

Yes and No, pressure downstairs is higher than upstairs. My watch measure Barometric Pressure and is sensitive enough that if I have it on Altitude that it will give me the feet difference between down/up stairs.
itsme
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Re: Calibrating a Barometer

Quote from: Strat
Fortunately I have a semi-pro weather station with an accurate Barometer.

The majority are accurate but still have to be referenced as the pressure quoted for weather is referenced to sea level. I'm off skiing tomorrow and I know that the pressure will be around 600 when the weather pressure is around 1200. So if you have a Barometer in a ski resort you will still set it to 1200.