What is "normalhohennull"

("standard elevation zero") or NHN is a standard reference level, the equivalent of sea level, used in Germany to measure height.

In geographical terms, NHN is the reference plane for the normal height of a topographical eminence height above mean sea level used in the 1992 German Mean Height Reference System (). The plane is in the shape of a quasi- geoid. The reference height is a geodetic, fixed point on the New Church of St. Alexander at Wallenhorst in the German state of Lower Saxony. The geopotential height of this point was calculated in 1986 as part of the United European Levelling Network (UELN), based on the Amsterdam Ordnance Datum, which represents the average level of the North Sea.