Set the barometer correctly - you should know that

The barometer is used to measure atmospheric air pressure in hPa. Air pressure can be understood as the weight of an air column that extends from the surface of the earth to the upper layers of the atmosphere. Due to the different warming of latitudes, the arrangement of continents and seas as well as movement processes in the atmosphere, the distribution of air pressure is uneven. At sea level, it averages 1013.25 hPa worldwide. It mostly fluctuates between 990 and 1040 hPa.

The deformation of a flat, airless metal can is used to measure the atmospheric air pressure. Rising air pressure compresses the can, and when the air pressure falls, it expands again. This movement, which is only a few hundredths of a millimeter, is transferred to the pointer with the help of a fine mechanism, thus displaying the air pressure.

Why does a barometer have to be set?

The air layer above and with it the air pressure decrease with increasing altitude, about 1 hPa per 8 m height difference near the earth. In order to obtain comparable air pressure values, all data are related to sea level in the weather observation. This means that the pressure actually present on site (absolute air pressure) is converted to the level of the sea level (reduced air pressure), the influence of the altitude on the air pressure is thus corrected.

Setting the barometer to the operating height

The barometer is set in the manufacturer's factory for the height specified on the packaging. Only in rare cases will it be possible to use the barometer without having to reset it. The principle of adjustment to the altitude of use is to compensate for the change in air pressure caused by changing the altitude by correcting the pointer position in the opposite sense. If the location is lower than the preset height, the pointer must be adjusted to the lower pressure. If the place of use is higher than the preset height, the adjustment to the higher pressure must be made.

The easiest way to set the barometer correctly is to set it according to the air pressure information 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 decreases with increasing altitude by 1 hPa per 8 m difference in altitude.

Example: The set height is 200 m, the height of the location is 40 m. The height difference is therefore 160 m. An adjustment of the pointer by 160 m: 8 m / hPa = 20 hPa to the low pressure is required to compensate for the increase in air pressure by 20 hPa.

Depending on the type of barometer, its manual setting is carried out in a different way. The high-quality precision can or aneroid barometers have an opening on the rear wall on which the brass adjusting screw is located. If you turn this, the pointer of the barometer will move. When setting the barometer correctly, you should always use the shortest route to the determined value clockwise or counterclockwise.

Since the air pressure is always the same in closed rooms as outdoors, the barometer can be attached anywhere in the room. However, we recommend that you do not hang the barometer on an outside wall or near a heater. This applies in particular to barometers that are combined with a thermometer and hygrometer to form a weather station. This is the only way that thermometers and hygrometers display genuine values.