The barometer is used to measure the atmospheric air pressure in hPa. The atmospheric pressure can be understood as the weight of a column of air that extends from the surface of the earth to the upper layers of the atmosphere. Due to the different warming of the latitudes, the arrangement of continents and oceans as well as movement processes in the atmosphere, the distribution of the air pressure is uneven. At sea level, the global average is 1013.25 hPa. For the most part it fluctuates between 990 and 1040 hPa.
To measure atmospheric air pressure, the deformation of a flat, airless metal can is used. Increasing air pressure compresses the can, while decreasing air pressure expands it again. This movement, which is only a few hundredths of a millimetre, is transferred to the pointer by a fine mechanism and the air pressure is displayed.
Why does a barometer have to be adjusted?
With increasing altitude, the layer of air above decreases and with it the air pressure, in the vicinity of the earth about 1 hPa per 8 m altitude difference. In order to obtain comparable air pressure values, all data in weather observation are referred to sea level. This means that the pressure actually existing on site (absolute air pressure) is converted to sea level (reduced air pressure); the influence of the altitude on the air pressure is thus corrected.
Adjusting the barometer to the operating altitude
Barometer is set at the factory for the altitude indicated on the packaging. Only in rare cases will it be possible to use the barometer without readjustment. The principle of adjustment to the operating altitude is to compensate for the change in air pressure caused by changing the altitude by correcting the pointer position in the opposite direction. If the altitude of the place of use is lower than the pre-set altitude, the pointer must be adjusted towards the lower pressure. If the location of use is higher than the pre-set altitude, the pointer must be adjusted towards the higher pressure.
The easiest way to adjust the barometer correctly is to set it according to the air pressure information given in the weather report. If the altitude of the place of use is known exactly, the correction value can also be calculated. The calculation is based on the fact that the air pressure increases with increasing altitude by 1 hPa per 8 m height difference decreases.
Example: The set height is 200 m; the height of the site is 40 m. The difference in height is therefore 160 m. An adjustment of the pointer by 160 m: 8 m/hPa = 20 hPa to the lower pressure is necessary to compensate for the increase in air pressure by 20 hPa.
Depending on the type of barometer, its manual adjustment is done in a different way. FISCHER's high-quality precision mechanical can or aneroid barometers have an opening on the rear wall where the brass adjustment screw is located. If you turn this, the pointer of the barometer is adjusted. When adjusting the barometer correctly, you should always use the shortest route to the measured value in a clockwise or counter clockwise direction.
Since the air pressure in closed rooms is always the same as outside, the barometer can be installed anywhere in the room. However, we recommend that you do not hang the barometer on an outside wall or near a heater. This is especially true for barometers that are combined with a thermometer and hygrometer to form a weather station. This is the only way to ensure that thermometers and hygrometers display unaltered values.
Buy different precise barometers from FISCHER
FISCHER's high quality, precision mechanical barometers are handmade in our own factory and can be ordered in our online shop. They reliably indicate the level of atmospheric air pressure and also convince with their noble design.
You are welcome to have a look at the different models of barometers in the FISCHER range! You will also find climate meters or watches in the shop.
If you have any questions about our products or the correct adjustment of a barometer, you can of course contact us at any time. Our competent staff will be happy to advise you and will reliably take care of your request.