A dot matrix printer apparatus has a magnetic ink jet recording head which projects a continuous stream of ferro-fluid ink drops toward a print medium. The ink drops are rastered in the direction orthogonal to the direction of relative motion of the recording head and the print medium to form characters...http://www.google.de/patents/US4075636?utm_source=gb-gplus-sharePatent US4075636 - Bi-directional dot matrix printer with slant control
