PDA

View Full Version : Boring barometer question



sasquatch
15-09-2010, 16:28
Sorry for such a mundane question but I've bought an art deco barometer off ebay. :rolleyes: It's obviously 70-80 years old, I don't know where it's from and got to thinking how do I set it properly?

I'm at roughly 200 metres above sea level but don't know what the barometer is set at and I have no idea how to zero it...will it still perform alright not being set to my immediate atmospheric pressure/ elevation?

Thanks in advance if anyone has any ideas. Cheers, Chad

Stamp
15-09-2010, 16:32
Im not expert but mine is in the hall and has no adjustment on it that I know of.....

sasquatch
15-09-2010, 16:47
Mine's got a tiny screw in the back to adjust it with. I'm as far from expert as you can get with these things, I just got it because I decided it would look good in the newly decorated hallway...

southey
15-09-2010, 16:53
i'm only guessing here, but you could put it up where it's going to live, now guessing that it has pressure grades marked on it, let it settle for a week or so, then using the met office's pressure chart for up to date figures relating to where you are, you could try adjusting to that figure? or if it's the kind that says the kind of weather your likely to have, wait for it to rain then adjust it to rain, and watch to see if it predicts the rest?

Andy2112
15-09-2010, 17:01
i'm only guessing here, but you could put it up where it's going to live, now guessing that it has pressure grades marked on it, let it settle for a week or so, then using the met office's pressure chart for up to date figures relating to where you are, you could try adjusting to that figure? or if it's the kind that says the kind of weather your likely to have, wait for it to rain then adjust it to rain, and watch to see if it predicts the rest?

Spot on Southey, just look at the pressure charts on the met office website, that's how i did mine Chad.

bilmo-p5
15-09-2010, 17:02
You can check your baro's pressure reading against that of a local observing station. Met Off says Cottesmore is the nearest to you ... http://www.metoffice.gov.uk/weather/uk/em/cottesmore_latest_weather.html

If you check it regularly over a couple of days or a week, the difference between your reading and Cottesmore's reading at any given time should remain pretty much the same if your baro is working correctly. Once you have established and average difference it is no problem to correct your readings.
The main advantage of a barometer is not so much to see the pressure at a given time as to enable the observer to determine the change and rate-of-change of the local barometric pressure; the barometric trend. This trend is valuable indicator in weather forecasting. Even if your baro is consistently high or low on the actual pressure the trend will be the same. Most baros have a manual pointer which you can move to the current pressure when you read it so that the next time yo read it you can tell at a glance whether the pressure is rising or falling.

Bushwhacker
15-09-2010, 17:06
If I'm thinking right, 200m above sea level will mean that the pressure is 20 millibars less than pressures given at sea level - working at 10 meters elevation per millibar (I think)
See if you can borrow a calibrated barometer and check it against that. It may be correct already. As for setting it, I don't know

sasquatch
15-09-2010, 17:47
Thanks for that guys, I didn't even think to check the local observing station...:sleeping:Der!:sleep ing: Der! I'll get on that one.

IanM
15-09-2010, 18:29
An aneroid barometer (small and the commonest) will have a tiny screw through a hole in the back. Set the reading to the same as your local weather station on a clear, calm day when the pressure is constant for a few hours. Don't allow for your height as all readings are referenced back to sea level and that is already the reading from your local WS. One problem you probably will have is converting from millibars from your local report to inches of mercury which I assume your old barometer is calibrated for, but there are plenty of converters on the internet.

A mercury barometer (long and large) will already be naturally calibrated but the reading will need to be adjusted to allow for your height so the readings match your local WS. This will probably have to be via a inch of mercury to millibar conversion chart in excel (not too difficult to construct).

If it is any other type you might be sitting on a goldmine and a photo would help.

Wayland
15-09-2010, 18:55
Just to add to what has already been said, Make the adjustment during a stable period of high pressure for the best results.

sasquatch
15-09-2010, 21:38
Thanks again for all the help fellas! I doubt it's anything fancy, I'm not generally lucky with that sort of thing...

http://i640.photobucket.com/albums/uu123/bustyaleep/barometer.jpg

I just got it because I've been doing a lot of diy and decorating and wanted to put up something useful as well as asthetically pleasing in my opinion instead of just stuff my wife wants. Give and take and all that! Cheers

Zingmo
15-09-2010, 22:30
See if you can get hold of a Zambretti Forecaster - I use mine with my barometer a lot and it is at least as good as the BBC!

Z