Caspian Sea of around 149,200 square miles (386,400 square km)— bigger than the region of Japan—and its surface lies somewhere in the range of 90 feet (27 meters) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on earth after Lake Baikal (−1,180 m, −3,871 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size. The sea has a surface area of 371,000 km (143,200 sq mi) (not including the detached
Sea level sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. "Still-water level" or "still-water sea level" (SWL) is the level of the sea with motions such as wind waves averaged out. Then MSL implies the SWL further