The Sacconi iso line layout of the
"back arch" as an assumption to render
an "average" Stradivarius arch shape.
This figure shows Sacconis attemt to construct a 3D model by 2D geometric layouts for a "back" arch shape of an average Stradivarius violin. It seems obvious that it is a 2D-construction since all intersection points are positioned on circular arcs intersecting straight lines. The picture is divided into 4 sectors marked by the 4 congruent shaped "beams" on the surface. Within the waist sector circumscribed by these 4 line there is complete congruence of shape not only comparing left and right but also up and down.. The dividing angle marks out the image line of the congruent picture. It is not possible to find any connection between the "upper" and "lower" sectors. The center of the "element" image is not in the center of the arch shape. No equal "elements" can be found covering the "upper" and "lower" parts of the shell. Only a limited sector in the "waist" has this quality.