Mean High -Water Springs. Mean height of spring high waters at a place when deduced from an adequate number of observations.
Mean Latitude. That latitude whose numerical value is half the sum of a latitude left and a latitude reached.
Mean Low Water. Mean of all low waters at a place when observed during a lunation of 29 days.
Mean Low-Water Springs. Mean height of spring low waters at a place when deduced from an adequate number of observations.
Mean Noon. Instant in which Mean Sun is on meridian of a place.
Mean Place of Star. That position on the celestial concave at which a star would appear to be if viewed from Sun. It is expressed in declination north or south of Equinoctial and sidereal time angle from First Point of Aries on January 1 of current year.
Mean Sea Level. Level that sea would maintain if no tidal effect were manifested and average meteorological conditions prevailed. For hydrographic and surveying purposes the level is derived from very prolonged and careful observations at an appropriate position - Newlyn, Cornwall, being selected for British standard level.
Mean Solar Day. Interval between successive transits of Mean Sun across a given meridian. Its length is the mean length of all apparent solar days in a year.