Instruments drawing conic sections are described by B. Cavalieri ( "Specchio Ustorio" i.e."The burning mirror", Bologna 1638). In fact (as Cavalieri says) they were invented by Paciotti and were builted by M.Oddi. Here you can see the machine drawing the ellipse: VTR is a right-angled triangle: VT is the "latus rectus" and VR is the greater axis of the ellipse we want to draw. The rectangular sheet (of plexiglas) BCDE moves on three rails parallel to TR and during the motion the side BC is perpendicular to VR. BC and TR intersect in Q and BD and VR ntersect in H . The triangle QHA is right-angled and QH=HA; a pin with a cursor moving on VR is put on A .The vertex P of the squareAPV moves on the rail BC the side PV rotates around the pivot V . A style placed in P, during the motion draws an ellipse.