Nicomedes's Mechanism for Constructing a Conchoid
This Demonstration gives Nicomedes's (c. 180 BC) mechanism for constructing a conchoid. The mechanism consists of three rulers. Two are perpendicular; the horizontal one has a slot and the vertical one has a fixed peg at . The third ruler, , has a fixed peg at that slides along and a slot that lets it slide along .[more]
You can vary the distance between the points and B and the length .[less]
 T. L. Heath (ed.), The Works of Archimedes, New York: Dover Publications, 2002, p. cvii.
 D. E. Smith, History of Mathematics, Vol. II, New York: Dover Publications, 1958, pp. 299–300.