The German horizontal (also Frankfurt one horizontal, Frankfurt horizontal plane, Tragus Orbita line, Orbitomeatallinie) is a term from anatomy. The meant horizontal line, which runs by the tiefstgelegenen point of the Unterrandes of the eye socket and by the highest point of the outside Gehrgangs (Porus acusticus externus, Porion) in the human head, was defined 1882 by Anthropologen on a congress in Frankfurt/Main for the Kraniometrie. Today it still serves as attitude level for radiographs and computer tomographies of the head, as well as datum plane in the dental medicine.
As datum line in anatomy also the Basilarlinie (Reid's LINE) finds, a meant line to use by the center of the outside and the outside eye angle.
Another head datum plane in the dental medicine is the Camper' level by the Porion and the Nasospinale (Spina nasalis anterior).