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  2. Sea level - Wikipedia

    en.wikipedia.org/wiki/Sea_level

    Height above mean sea level (AMSL) is the elevation (on the ground) or altitude (in the air) of an object, relative to a reference datum for mean sea level (MSL). It is also used in aviation, where some heights are recorded and reported with respect to mean sea level (contrast with flight level ), and in the atmospheric sciences , and in land ...

  3. Chart datum - Wikipedia

    en.wikipedia.org/wiki/Chart_datum

    A chart datum is the water level surface serving as origin of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. [1] Common chart datums are lowest astronomical tide (LAT) [1] and mean lower low water (MLLW).

  4. Height above mean sea level - Wikipedia

    en.wikipedia.org/wiki/Height_above_mean_sea_level

    Height above mean sea level is a measure of a location's vertical distance (height, elevation or altitude) in reference to a vertical datum based on a historic mean sea level. In geodesy, it is formalized as orthometric height. The zero level varies in different countries due to different reference points and historic measurement periods.

  5. Density altitude - Wikipedia

    en.wikipedia.org/wiki/Density_altitude

    This is an easier formula to calculate ... , atmospheric pressure in millibars (mb) adjusted to mean sea level; , outside air temperature in ...

  6. Benchmark (surveying) - Wikipedia

    en.wikipedia.org/wiki/Benchmark_(surveying)

    The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark.A fundamental benchmark is a point with a precisely known relationship to the vertical datum of the area, typically mean sea level.

  7. Reduced level - Wikipedia

    en.wikipedia.org/wiki/Reduced_level

    Countries adopt their nearby mean sea levels as datum planes for calculations of reduced levels in their respective jurisdictions. For example, Pakistan takes sea near Karachi as its datum while India takes sea near Mumbai as its datum for calculation of reduced levels. The term reduced level is denoted shortly by 'RL'.

  8. Standard sea-level conditions - Wikipedia

    en.wikipedia.org/wiki/Standard_sea-level_conditions

    Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations. The term "standard sea level " is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.

  9. Pressure altitude - Wikipedia

    en.wikipedia.org/wiki/Pressure_altitude

    In aviation, pressure altitude is the height above a standard datum plane (SDP), which is a theoretical level where the weight of the atmosphere is 29.921 inches of mercury (1,013.2 mbar; 14.696 psi) as measured by a barometer. [2]