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Guest
Guest
How does one Calibrate a Barometer? Am I being dense? /forums/images/graemlins/confused.gif
peteandthira
Well-Known Member
Ha Ha! You can't escape me.
Phone a local met office (airport possibly) and ask for a barometer setting (known as a QFF, in military met banter).
I have tame met forecaster friends who will do that for me, but we need to synchronise it to make sure the timing is right.
Yaboo sucks! /forums/images/graemlins/grin.gif
Phone a local met office (airport possibly) and ask for a barometer setting (known as a QFF, in military met banter).
I have tame met forecaster friends who will do that for me, but we need to synchronise it to make sure the timing is right.
Yaboo sucks! /forums/images/graemlins/grin.gif
peteandthira
Well-Known Member
Smiffy
PS to the above, you would also have to give me your location. I am not sure you want to do that....
PS to the above, you would also have to give me your location. I am not sure you want to do that....
lenseman
Well-Known Member
- Joined
- 3 Jun 2006
- Messages
- 7,077
- Location
- South East Coast - United Kingdom
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Guest
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GULP!!! Oooooooeeeeeeerrrrrrrr Mother! I've got the Navy and the perishin' Airforce after me now!
Thanks to you both, I will have a look at the site (Captain Lenseman Sir) and to Pops, Just pitch up at Bideford, and ask for the village idiot, everybody knows me, (well, not if they have got any sense they don't) /forums/images/graemlins/crazy.gif /forums/images/graemlins/grin.gif
Thanks to you both, I will have a look at the site (Captain Lenseman Sir) and to Pops, Just pitch up at Bideford, and ask for the village idiot, everybody knows me, (well, not if they have got any sense they don't) /forums/images/graemlins/crazy.gif /forums/images/graemlins/grin.gif
peteandthira
Well-Known Member
Smiffy
You can also just download the latest synoptic chart (1200 UTC, say, having noted your barometer reading AT 1200 UTC) and estimate the pressure at your location from the isobars. Then just apply the difference between your recorded reading at 1200, and the synoptic chart ACTUAL at 1200.
I am under red wine at the moment, and the above might be tricky if you aren't sure of met banter.
I will of course be of the utmost assistance by PM if required!
Pops
You can also just download the latest synoptic chart (1200 UTC, say, having noted your barometer reading AT 1200 UTC) and estimate the pressure at your location from the isobars. Then just apply the difference between your recorded reading at 1200, and the synoptic chart ACTUAL at 1200.
I am under red wine at the moment, and the above might be tricky if you aren't sure of met banter.
I will of course be of the utmost assistance by PM if required!
Pops
lenseman
Well-Known Member
- Joined
- 3 Jun 2006
- Messages
- 7,077
- Location
- South East Coast - United Kingdom
Although Ilfracombe seems to be down at the moment, Bude works on the following link:
http://www.weatherstations.co.uk/aws_map.htm
http://www.weatherstations.co.uk/aws_map.htm
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Guest
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Thanks once again both, just got to unscrew Barometer from bulkhead, and see if there is a screw to twiddle, is that how you do it? (I'm not very bright, shouldn't be allowed out really) /forums/images/graemlins/smile.gif
Thistle
Well-Known Member
This is best done when we are under a dirty great big high pressure system so there is very little difference across the country. To do it properly, though, you still have to make the appropriate corrections for altitude and temperature.
It's worth remembering that, for most of the time, sailors will be interested in changes of pressure (fast change ... steep pressure gradient ... high wind and vice versa) rather than in the actual pressure itself so an uncalibrated barometer is likely to be perfectly acceptable.
It's worth remembering that, for most of the time, sailors will be interested in changes of pressure (fast change ... steep pressure gradient ... high wind and vice versa) rather than in the actual pressure itself so an uncalibrated barometer is likely to be perfectly acceptable.
peteandthira
Well-Known Member
"This is best done when we are under a dirty great big high pressure system so there is very little difference across the country. To do it properly, though, you still have to make the appropriate corrections for altitude and temperature.
It's worth remembering that, for most of the time, sailors will be interested in changes of pressure (fast change ... steep pressure gradient ... high wind and vice versa) rather than in the actual pressure itself so an uncalibrated barometer is likely to be perfectly acceptable."
I agree with you mostly, although it isn't necessary to have a huge high over us. An uncalibrated barometer is indeed as useful as a calibrated one as long as it doesn't run off it's scale.
You can still get to within 1mb from my technique, as long as you have made a note of your barometer reading at the time that the current analysis is produced. All you need to do then is to tweak your instrument (fnarr, fnarr) for the difference you saw at the time.
Sorry, I'm getting banter from the missus to leave this alone - but will be happy to pursue this tomorrow. I have better met knowledge than I have sailing knowledge!
BFN
Pops
It's worth remembering that, for most of the time, sailors will be interested in changes of pressure (fast change ... steep pressure gradient ... high wind and vice versa) rather than in the actual pressure itself so an uncalibrated barometer is likely to be perfectly acceptable."
I agree with you mostly, although it isn't necessary to have a huge high over us. An uncalibrated barometer is indeed as useful as a calibrated one as long as it doesn't run off it's scale.
You can still get to within 1mb from my technique, as long as you have made a note of your barometer reading at the time that the current analysis is produced. All you need to do then is to tweak your instrument (fnarr, fnarr) for the difference you saw at the time.
Sorry, I'm getting banter from the missus to leave this alone - but will be happy to pursue this tomorrow. I have better met knowledge than I have sailing knowledge!
BFN
Pops
VicS
Well-Known Member
In addition to the Skylinkweather site XC Weather is a good source of of data.
Plenty of other online weather stations as well. However if you want an accurate reading use "Official "stations rather than, for example, yacht clubs as the pressure readings are often way out on those.
IMHO it is better to calibrate your barometer when the pressure is close to its mean value of 1013mb rather than at an extreme such as when " when we are under a dirty great big high pressure system"
Remember that if you are setting your barometer at home, but intend to use it on the boat, to allow to for your altitude. Pressure falls by 11.4 mb / 100m. So if the sea level pressure given at your nearest weather station is 1013 and you are 100m above sea level you must set it to read 1001.6mb
Plenty of other online weather stations as well. However if you want an accurate reading use "Official "stations rather than, for example, yacht clubs as the pressure readings are often way out on those.
IMHO it is better to calibrate your barometer when the pressure is close to its mean value of 1013mb rather than at an extreme such as when " when we are under a dirty great big high pressure system"
Remember that if you are setting your barometer at home, but intend to use it on the boat, to allow to for your altitude. Pressure falls by 11.4 mb / 100m. So if the sea level pressure given at your nearest weather station is 1013 and you are 100m above sea level you must set it to read 1001.6mb
Oen
Well-Known Member
Sorry, QFF (known colloquially as 'For Forecasters') is QFE (station pressure at the highest point on the manoeuvring area) reduced to sea level using ambient conditions, and is very rarely used or spoken of. QNH (widely used and available) is QFE reduced using the standard atmosphere. Either will be absolutely fine. Comments above about high pressure are very apposite.
bilbobaggins
N/A
You can plug into the system provided by a grateful nation, more or less since Admiral Beaufort ran his office in Whitehall....
Most - if not all - harbourmasters were/are required to maintain an accurate, corrected barometer available as a reference for mariners. So toddle along to your local Harbour Office and ask. You may find the easiest way is to telephone by arrangement, get the reading already corrected by him for temperature and elevation above MSL, and compare this with your own instrument. Most aneroid ( capsule ) instruments have a means of adjustment, and do bear in mind that 30 feet change of altitude equates to 1 HPa ( 1 Millibar in old money )
Don't expect this to work accurately if you are in a different harbour from the one being used as reference.
Many Harbourmasters are retired Master Mariners, and are only too pleased to find a yottie taking a 'pro level' interest in what was their specialisation. The chaps at Ilfracombe and Padstow are first-rate, for example, while the fellow at Bristol Floating Harbour may well not know what a barometer is, never mind know how to read one......
( leads with chin! )
/forums/images/graemlins/grin.gif
( Or, as OEN suggests above, find a friendly Training Captain on Multi-Engine Jet Aircraft, cross his palm with Heineken, and weeble that you 'don' unnerstand this stuff'.... then stand back! )
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
Most - if not all - harbourmasters were/are required to maintain an accurate, corrected barometer available as a reference for mariners. So toddle along to your local Harbour Office and ask. You may find the easiest way is to telephone by arrangement, get the reading already corrected by him for temperature and elevation above MSL, and compare this with your own instrument. Most aneroid ( capsule ) instruments have a means of adjustment, and do bear in mind that 30 feet change of altitude equates to 1 HPa ( 1 Millibar in old money )
Don't expect this to work accurately if you are in a different harbour from the one being used as reference.
Many Harbourmasters are retired Master Mariners, and are only too pleased to find a yottie taking a 'pro level' interest in what was their specialisation. The chaps at Ilfracombe and Padstow are first-rate, for example, while the fellow at Bristol Floating Harbour may well not know what a barometer is, never mind know how to read one......
( leads with chin! )
/forums/images/graemlins/grin.gif
( Or, as OEN suggests above, find a friendly Training Captain on Multi-Engine Jet Aircraft, cross his palm with Heineken, and weeble that you 'don' unnerstand this stuff'.... then stand back! )
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
peteandthira
Well-Known Member
bilbo
"( Or, as OEN suggests above, find a friendly Training Captain on Multi-Engine Jet Aircraft, cross his palm with Heineken, and weeble that you 'don' unnerstand this stuff'.... then stand back! )"
He was already doing that, in a way. I was an RAF pilot for 26 years, and taught local meteorology (as well as flying) to trainee flying instructors at the RAF's Central Flying School for the last few. All I have said in my posts is correct.
Pops
"( Or, as OEN suggests above, find a friendly Training Captain on Multi-Engine Jet Aircraft, cross his palm with Heineken, and weeble that you 'don' unnerstand this stuff'.... then stand back! )"
He was already doing that, in a way. I was an RAF pilot for 26 years, and taught local meteorology (as well as flying) to trainee flying instructors at the RAF's Central Flying School for the last few. All I have said in my posts is correct.
Pops
peteandthira
Well-Known Member
Smiffy
Note your barometer reading at 1200 today. Then tell me your barometer's location. I will do it for you!
You need to find the adjustment screw though, I can't help you with that.
Pops
Note your barometer reading at 1200 today. Then tell me your barometer's location. I will do it for you!
You need to find the adjustment screw though, I can't help you with that.
Pops
Sinbad2222
Well-Known Member
Why does a yachtsman need to know the barometric pressure so accurately? It's the change in pressure over time that is important, surely the absolute value is irrelevant?
Oen
Well-Known Member
If the forecast suggests that the pressure will be a certain value, say, at the centre of a low pressure system, then accurate knowledge of the instant pressure will help with orientation within that system.
G
Guest
Guest
Very many thanks to all that have responded to my enquiry. Very interesting, not withstanding the technical stuff, I just felt that if I was going to have the thing dangling on the bulkhead, it might as well be as accurate as possible?
Pops, I may take you up on your offer, if my local Harbourmaster can't help?
Once again, many thanks.
Smiffy.
Pops, I may take you up on your offer, if my local Harbourmaster can't help?
Once again, many thanks.
Smiffy.
peteandthira
Well-Known Member
Smiffy
No problem. Did you note your reading at 1200? If not, get one at any 6-hr interval and let me know the time and the reading
sinbad is quite right, you don't need to have a spot-on reading, but I will get you to within 2mb.
Pops
No problem. Did you note your reading at 1200? If not, get one at any 6-hr interval and let me know the time and the reading
sinbad is quite right, you don't need to have a spot-on reading, but I will get you to within 2mb.
Pops
peteandthira
Well-Known Member
PS - Oen is right too. 2mb is quite close enough for that too, IMHO.
Pops
Pops