# Who uses the barometric pressure? **URL:** \ **Category:** Factual Questions\ **Created:** [May 24, 2009, 4:35pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469 "2009-05-24T16:35:07Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Papa\_D\_Bear](https://avatars.discourse-cdn.com/v4/letter/p/b5ac83/32.png) [@Papa\_D\_Bear](https://boards.straightdope.com/u/Papa_D_Bear)\ **Post date:** [May 24, 2009, 4:35pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/1 "2009-05-24T16:35:07Z")
All the weather reports I encounter, print - tv - web, state the current pressure. I can appreciate the usefulness of the trending. Dropping that a low is coming or Rising that a high is approaching. I also remember from piolt training that the current air pressure at ground level being used to correct my altitude calculation. At the time of this posting, here in Toronto the air pressure is 101.8 kPa Who uses this information that it is consistently reported in all weather reports? ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [May 24, 2009, 5:14pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/2 "2009-05-24T17:14:55Z")
Yes, I agree that the trend is more useful than the absolute value… but if you know that the average is around 100 kPa, then you can see whethe it’s more likely to rise or fall. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 24, 2009, 6:22pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/3 "2009-05-24T18:22:20Z")
Surveyors need it to adjust the distance calibration on EDM (electronic distance measurement) devices, like the cyan or yellow optical instruments you often see them looking through (I mean the more powerful ones with boxy looking sides and a little telescope in the middle). I was looking for barometric pressures briefly last week to test an idea about beta radiation pentrating an air gap. I think pilots use, or used to use, barometric pressure to adjust altimeters - but I’m not sure, maybe they only compensate for it by adjusting the altimeter at known altitudes. ---
**Author:** ![PaulParkhead](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@PaulParkhead](https://boards.straightdope.com/u/PaulParkhead)\ **Post date:** [May 24, 2009, 6:52pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/4 "2009-05-24T18:52:55Z")
> [@Napier](#): > > I think pilots use, or used to use, barometric pressure to adjust altimeters - but I’m not sure, maybe they only compensate for it by adjusting the altimeter at known altitudes. Pilots do indeed use barometric pressure to calibrate their altimeters. Below certain altitudes, they use a figure supplied by ATC. Above these altitudes, they use a standardised setting. ---
**Author:** ![Public\_Animal\_No.9](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@Public\_Animal\_No.9](https://boards.straightdope.com/u/Public_Animal_No.9)\ **Post date:** [May 25, 2009, 1:07am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/5 "2009-05-25T01:07:54Z")
It’s also useful in numerous technical and scientific studies. Boiler efficiency studies sometimes use barometric pressure, for instance. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [May 25, 2009, 1:27am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/6 "2009-05-25T01:27:43Z")
> [@Napier](#): > > I think pilots use, or used to use, barometric pressure to adjust altimeters - but I’m not sure, maybe they only compensate for it by adjusting the altimeter at known altitudes. It doesn’t matter what altitude you’re at when you adjust the altimeter. If you couldn’t do it at altitude there would be no way of knowing what your altitude is as you fly through different pressure areas. Nothing worse than seeing [mountain goats](http://pw0nd.com/2009/01/06/mountain-goat/) outside your window. ---
**Author:** ![Aji\_de\_Gallina](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aji_de_gallina/32/260_2.png) [@Aji\_de\_Gallina](https://boards.straightdope.com/u/Aji_de_Gallina)\ **Post date:** [May 25, 2009, 1:58am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/7 "2009-05-25T01:58:54Z")
> [@Public\_Animal\_No.9](#): > > It’s also useful in numerous technical and scientific studies. Boiler efficiency studies sometimes use barometric pressure, for instance. Sure, but the people who really need barometic pressure don’t get it from the morning news, they have good and accurate instruments. I have no use at all for that information. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [May 25, 2009, 2:46am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/8 "2009-05-25T02:46:09Z")
> [@PaulParkhead](#): > > Pilots do indeed use barometric pressure to calibrate their altimeters. Below certain altitudes, they use a figure supplied by ATC. Above these altitudes, they use a standardised setting. To amplify, the “altimeter setting” is the local sea-level pressure at the reporting location (what the pressure would be if you dug a hole from there down to sea level). Diligence at adjusting their altimeters keeps everyone actually at the altitude they think they’re at, which is helpful for preventing unpleasantnesses from occurring. It also lets everyone know how high above the ground they are, since the ground may be rough but its elevation is known. Above 18,000 feet (in the US, anyway), everyone sets their altimeters to the same standard setting (29.92 inches of mercury, btw), to avoid the bother of constantly adjusting it, and because there’s hardly any land up there to run into anyway. Up there, pilots speak of “flight levels” instead of altitude. A flight level is the indicated altitude with the setting at 29.92, divided by 100. FL330 may be higher or lower than 33,000 actual feet, for instance, but everyone at that flight level will be at the same altitude anyway. In some large wilderness areas, like northern Canada, there are too few reporting stations on the ground to get a useful setting anyway, so everyone uses 29.92 at all altitudes and keeps track of height above the ground visually. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [May 25, 2009, 2:47am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/9 "2009-05-25T02:47:42Z")
> [@Aji\_de\_Gallina](#): > > Sure, but the people who really need barometic pressure don’t get it from the morning news, they have good and accurate instruments. > I have no use at all for that information. Generally, high pressure = clear weather, low pressure = bad weather, and not everyone has a window handy. ---
**Author:** ![Spoons](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spoons/32/3141_2.png) [@Spoons](https://boards.straightdope.com/u/Spoons)\ **Post date:** [May 25, 2009, 3:54am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/10 "2009-05-25T03:54:22Z")
> [@ElvisL1ves](#): > > Generally, high pressure = clear weather, low pressure = bad weather, and not everyone has a window handy. This is how I use the barometric pressure as reported. I know what normal barometric pressure is, and the reported figure, as well as the trend in pressure (“the barometer is falling,” “the barometer is rising”) gives me an idea whether I should expect fair weather or stormy weather. ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [May 25, 2009, 6:51am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/11 "2009-05-25T06:51:42Z")
I use it to decide how long I must boil my eggs. ---
**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\ **Post date:** [May 25, 2009, 7:51am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/12 "2009-05-25T07:51:48Z")
> [@Spoons](#): > > This is how I use the barometric pressure as reported. I know what normal barometric pressure is, and the reported figure, as well as the trend in pressure (“the barometer is falling,” “the barometer is rising”) gives me an idea whether I should expect fair weather or stormy weather. I have an electronic weather station and one function it has is collating changes in air pressure, temperature and humidity to give a fairly accurate weather forecast for the next couple of days. ---
**Author:** ![bluezooky](https://avatars.discourse-cdn.com/v4/letter/b/e8c25b/32.png) [@bluezooky](https://boards.straightdope.com/u/bluezooky)\ **Post date:** [May 25, 2009, 7:55am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/13 "2009-05-25T07:55:38Z")
As a recreational fisherman is something I keep an eye on, certainly a high pressure system will bring many species of freshwater fish on the bite, I’m sure it’s a factor pro fisherman consider. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 25, 2009, 10:51am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/14 "2009-05-25T10:51:00Z")
> [@ElvisL1ves](#): > > To amplify, the “altimeter setting” is the local sea-level pressure at the reporting location (what the pressure would be if you dug a hole from there down to sea level). Maybe you can answer a long-time question: when authorities report barometric pressure, do they mean the true pressure as measured at whatever altitude they happen to be? Or do they measure it and then apply a correction for their own altitude so it is an estimate of the pressure if you dug a hole, et c, as you describe? By “authorities” I guess I typically mean weather forecasters and reporters, and web sites that include it with other weather data, but I don’t really know who else reports barometric pressure and am curious about them too. In other words, does the reported barometric pressure work like the “altimeter setting” you describe? Or does the weather station in Denver always report really low barometric pressure? ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [May 25, 2009, 11:34am UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/15 "2009-05-25T11:34:25Z")
Official weather stations report _actual_ barometric pressure, not an adjusted one. The airports I tend to fly out of don’t have ATC, so I usually use whatever the equipment at the airfield is reporting, though on occasion I have used what is reported on the TV or regular radio. For what I do in the air, it’s sufficient. The only time I worry about getting official ATC altimeter settings is when I’m flying into a busy airport with ATC towers where there is definitely a real reason to use the same setting as everyone else. Interesting thing about small airplane altimeters - if you know the exact altitude of the runway you’re sitting on you can adjust it to read that altitude and thereby get the current barometric pressure. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [May 25, 2009, 1:38pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/16 "2009-05-25T13:38:51Z")
> [@Napier](#): > > when authorities report barometric pressure, do they mean the true pressure as measured at whatever altitude they happen to be? Yes. That’s why the altitude-corrected pressure is called an “altimeter setting”, not a pressure. ---
**Author:** ![PaulParkhead](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@PaulParkhead](https://boards.straightdope.com/u/PaulParkhead)\ **Post date:** [May 25, 2009, 6:23pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/17 "2009-05-25T18:23:06Z")
> [@ElvisL1ves](#): > > Above 18,000 feet (in the US, anyway), everyone sets their altimeters to the same standard setting (29.92 inches of mercury, btw), to avoid the bother of constantly adjusting it, and because there’s hardly any land up there to run into anyway. Up there, pilots speak of “flight levels” instead of altitude. A flight level is the indicated altitude with the setting at 29.92, divided by 100. FL330 may be higher or lower than 33,000 actual feet, for instance, but everyone at that flight level will be at the same altitude anyway. Thanks for that. Here in the UK transition altitude is only 6000 feet. Presumably that’s because the highest land-based obstruction is less than 4000 feet elevation. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [May 25, 2009, 6:32pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/18 "2009-05-25T18:32:44Z")
> [@Shamozzle](#): > > I use it to decide how long I must boil my eggs. At what altitude does one have to start to take ambient pressure into consideration for cooking? I live around 85 metres above sea level. Do I need to adjust boiling time? I don’t think so. What about 1000 metres (around 3900 feet)? 2,000 metres? ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [May 25, 2009, 9:53pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/19 "2009-05-25T21:53:44Z")
[All the links you need about high-altitude cooking](http://homecooking.about.com/od/altitude/High_Altitude_Cooking.htm). > [@](#): > > ``` > There is less (or lower) air pressure at high altitudes because the blanket of air is thinner than it would be at sea level. As a result, at sea level water, boils at 212' F; at an altitude of 7,500 feet, however, it boils at about 198' F because there is not as much air pressure to inhibit the boiling action. Foods will take longer to cook because they are actually cooking at a "lower" temperature. We should be aware that "boiling point" is also directly affected by purity of the water and will increase in proportion to the water hardness. It should also be noted that because of the lower air pressure, boiling water "evaporates" much more rapidly, causing the need for more liquid in cooking at higher elevations. This decreased air pressure means we must make adjustments in some ingredients and cooking time and also temperature. We must make adjustments in some of our cooking techniques as well, such as candy making, deep-fat frying and canning. In general, no recipe adjustment is necessary for yeast-risen baked goods, although allowing the dough or batter to rise twice before the final pan rising develops a much better texture and flavor. > You will find that beyond a certain altitude some foods cannot even be cooked without a pressure cooker! For instance, dried beans. The boiling point of water at very high altitudes is simply so low that without a pressure cooker the water will just keep steaming off at a temperature that doesn't even begin to cook the beans. > > ``` ---
**Author:** ![manila](https://avatars.discourse-cdn.com/v4/letter/m/e5b9ba/32.png) [@manila](https://boards.straightdope.com/u/manila)\ **Post date:** [May 25, 2009, 10:03pm UTC](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469/20 "2009-05-25T22:03:24Z")
> [@Aji\_de\_Gallina](#): > > Sure, but the people who really need barometic pressure don’t get it from the morning news, they have good and accurate instruments. > I have no use at all for that information. seconded, I have just started up a new gas pipeline in Northern Italy, To do this we had to buy gas from the local grid. We bought it in Standard Cubic Metres ( over one million) So it is imporatnt that I know the absolute pressure and temperature when calculating absolute volumes. But I dont depend on [weather.com](http://weather.com) We have our own instruments installed at the metering station [Next page](https://boards.straightdope.com/t/who-uses-the-barometric-pressure/497469.md?page=2)