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thumb|Sign referring to ' ("standard zero") or (short N. N. or NN') is an outdated official vertical datum used in Germany. Elevations using this reference system were to be marked (“meters above standard zero”). has been replaced by (NHN).

== History == In 1878 reference heights were taken from the Amsterdam Ordnance Datum and transferred to the New Berlin Observatory in order to define the 1879. has been defined as a level going through an imaginary point 37.000 m below . When the New Berlin Observatory was demolished in 1912 the reference point was moved east to the village of Hoppegarten| (now part of the town of Müncheberg|, Brandenburg, Germany).