Schematic plot of a warped disc according to the three warp models (see text): First row: simple Symmetric warp. Second row: Sine Lopsided warp. Third row: S Lopsided warp. Fourth row: S Lopsided warp with a twisted line-of-nodes. The red line shows the line-of-nodes and the orange sphere marks the position of the Sun. The blue line, perpendicular to the line-of-nodes, shows the maximum amplitude of the warp. The amplitude values for the schematic plot have been increased for the sake of clarity.