Barometer set up

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emnick

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Hello, I was lucky enough to receive a Weems & Plath barometer as a present. It is the Atlantis range Hi-Sensitiv.
It is calibrated in 'inHg' and also Kpa.
1) The Calibration starts from 29.5 inHg-30.5. is this range enough for sailing. I know we are looking for how quickly it drops etc.

2) The manual says it was adjusted at the factory at sea level, Should I be looking to re calibrate it when I get it on my boat. On this basis can I call up local coast guard for a pressure check, or is there a web site for different areas.

Thanks for any help
 
Hands off the screwdriver adjustmentr at the back of your instrument until there is a calibrated instrument close by to check yours with.

If you live close to a small airfield, they MAY check it for you or for that matter a local met office.

73s de
Johnth
 
If you wait till a big high is centred over your area with no iso bars over the country you should be able to compare its reading with met office station reports big highs often have the same pressure over the whole country
 
As you are in East Anglia, if you watch the BBC 6pm news, on the local weather section the lovely Julie Reiner usually gives a barometer setting check on Thursdays or Fridays - can't remember which offhand. Anyway it comes up every week. She says if it is a good week to set i.e. very slack pressure gradients, or not when sometimes she just gives an approximation if there is a steep pressure gradient across the region.

Anyway that is a local source for setting your lovely new instrument.
 
I'm pretty sure that the range is not sufficient for sailing in the UK. I'd expect a range between 27 and 31 ins. (my Lufft barograph went down to just below 960 millibars during the 1987 pseudo-hurricane.)

Perhaps the calibration range you quote is for a specific accuracy ?

You might also need to have a conversion table handy as most met details for pressure are in millibars, or more properly hPa (hectoPascals).

If you logon to the Met Office

http://www.metoffice.gov.uk/weather/uk/ee/ee_latest_pressure.html

you can see the present pressure gradient for Essex, and this will give you sufficient info to set your own instrument. No need to trouble CG or the nearest airport- they have a range of settings to account for height above sea level.
 
I agree with Sarabande The range will not be sufficient for sailing, or any other use, in the Uk.

29.5" is 999mb. The pressure can often go well below that!

30.5" is 1033mb. The pressure can go above that.

If it has been set for sea level that's what you want.

Reliable sources for pressure readings are

http://www.xcweather.co.uk/ (mostly from airport and airfield weather stations)

and the met office "latest weather" on http://www.metoffice.gov.uk/weather/uk/uk_latest_weather.html
or Sarabande's link

Ceefax page 404


There is a delay between the observation time and when these sources are up dated though .. check on the observation time.

Other "official" sources should give accurate readings but avoid Yacht club weather stations etc


All the above give the reading at sea level and if you check and or adjust your barometer it must be at sea level (if for boat use) when you do it or you must set it to read low by an amount equivalent to your height above sea level ( that can be appreciable .. at home here the barometer reads about 13 mb lower than the sea level pressure).

It is best to adjust your barometer when the pressure is steady (to eliminate the above time delay problems), as close as possible to the average pressure in the Uk of 1013 mb and of course when the pressure at your location is not likely to be significantly different to that at the weather station

BTW 1000mb = 100kPa
 
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Now taken a look at the Weems and Plath website.

According to that the Atlantis Hi-Sensitive has a range from 28.5 to 30.5 ! Now that is a bit more useful than one starting at 29.5.

Still only equivalent to 965 mb at the bottom end but at least usable. Below 965 mb most people would be sheltering in harbour and above 1033 you'll be enjoying the fine weather not watching the b***** barometer.

Check your scale again!
 
VicS said:
Still only equivalent to 965 mb at the bottom end but at least usable. Below 965 mb most people would be sheltering in harbour and above 1033 you'll be enjoying the fine weather not watching the b***** barometer.

Check your scale again!
Click to expand...

P1020556.jpg


10th March 2008. 958 mbar when the photo was taken, had been a little lower. I was a couple of thousand miles from the boat at the time.
 
To compare the OP's barometer with actual observations.

Since the on line barograph at NPL, Teddington was set up the pressure has been above 1033mb quite a few times, the max being about 1044 but it has only been below 965 3 times, the lowest being a touch over 960. Not been as low as 958 at Teddington.
It has been below 999mb (29.5") quite a lot
 
Thanks VicS

I just checked again, VicS is right, it is as he said 28.5inHg, I guess I will be seeing alot of needle movement with this unit! PS they also got me the clock to match. Beautiful bit of kit, will sit very nice on the boat
Thanks all.
 
OK boys (and girls) this is the bit I would like to know. I set my barometer at sea level with a calibrated instrument.

What difference will it make if I were at (say) 1,000 feet (up) and set my barometer with the same calibrated instrument?

73s de
Johnth
 
None.

The atmospheric pressure decreases by approx 11.4mb for every 100 metres above sea level. (at least to begin with)

sorry don't do feet ... they're flat things that stop the bottoms of your legs wearing


See Kaye and Laby on line http://www.kayelaby.npl.co.uk/general_physics/2_7/2_7_8.html

or Google for the info.

But if you set your barometer with a calibrated instrument at the same altitude they will read the same as each other whatever altitude you are at but they will only give the sea level pressure when at sea level. So the answer to your question is, "none."

My posh barometer is not corrected for altitude so at home it reads approx 13mb lower than the "sea level" pressure. If I take it down to sea level it reads the sea level pressure.
 
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Spot on VICS spot on. So, EMNICK hands off the screwdriver, your fine instrument has been calibrated at the factory.

Feet are good for me VICS, they have more divisions, half, third quarter etc.

73s de
Johnth
 
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