Geodesic
The Single Screw Reciprocal to the General Plane-Symmetric Six-Screw Linkage
Journal for geometry and graphics, Tome 1 (1997) no. 1, pp. 005-012 
J. E. Baker. The Single Screw Reciprocal to the General Plane-Symmetric Six-Screw Linkage. Journal for geometry and graphics, Tome 1 (1997) no. 1, pp. 005-012. http://geodesic.mathdoc.fr/item/JGG_1997_1_1_a1/
@article{JGG_1997_1_1_a1,
     author = {J. E. Baker},
     title = {The {Single} {Screw} {Reciprocal} to the {General} {Plane-Symmetric} {Six-Screw} {Linkage}},
     journal = {Journal for geometry and graphics},
     pages = {005--012},
     year = {1997},
     volume = {1},
     number = {1},
     url = {http://geodesic.mathdoc.fr/item/JGG_1997_1_1_a1/}
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Voir la notice de l'article provenant de la source Heldermann Verlag

The degree of mobility of a given linkage depends upon the order of its screw system, whereby a loop with six joint freedoms may be related to its reciprocal screw system, a single screw axis with an associated pitch. It has been postulated that this reciprocal screw can provide an alternative means of identifying its parent linkage, and an investigation in this respect has been recently carried out for the line-symmetric six-screw linkage. Here we undertake a similar enquiry for the plane-symmetric six-screw loop and so determine the essential characteristics of its reciprocal screw.