"Above sea level": from which sea this parameter is considered

Even from school geography lessons, we remember such a concept as "height above sea level." At the same time, at school, almost no one was told from which particular sea this value was considered. Could it be because they are all the same? Or is there still a difference between the seas on Earth? And if so, why only one (and quite specific) was chosen by scientists and sailors as a reference. All this will be discussed today.

Sea level is a very vague value. | Photo: robinwestenra.blogspot.com.

In geography, there is an absolute zero value, from which the height (or depth) of a geographic object is subsequently measured. Measurements are carried out on a scale from sea level. However, there are 63 seas on planet Earth. Given this fact, many citizens will probably be interested in whether all these reservoirs are at the same level, or if any of them is still a "reference" when calculating the height and depth. Everything is not easy here.

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Measured from the level of the Baltic Sea. | Photo: pixabay.com.

Many people forget that our planet does not look like a perfect ball. Therefore, the zero sea level in nature is constantly changing. It depends on a huge number of factors, including the rotation of the planet, atmospheric pressure and even specific coordinates. When performing complex calculations, sailors and scientists use an average zero indicator, which is calculated by specialists from the indicators of regular altitude measurements over the past 200 years.

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The levels are constantly changing. | Photo: yandex.uz.

In addition, there is a sea level reference value to simplify calculations. It is deducted based on the indicators of the Baltic Sea. Why exactly this? Everything is extremely simple here. At the beginning of the 20th century, surveyors established that due to the specifics of the geographical position, it is the Baltic Sea that demonstrates the lowest level of fluctuations in height. The daily and semidiurnal amplitudes of water here do not exceed 20 cm, which is negligible compared to other seas on Earth.