Orientation and motion of a discontinuity from single-spacecraft measurements of plasma velocity and density: Minimum mass flux residue - art. no. A03221 - Sonnerup,B; Haaland,S; Paschmann,G; Lavraud,B; Dunlop,MW; Rème,H; Balogh,A (JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 2004)