Peaucellier * (1864) discovered an exact straight-line mechanism of eight bars and
six pins, shown in Figure 3-2ge. Links 5, 6, 7, 8 form a rhombus of convenient size.
Links 3 and 4 can be any convenient but equal lengths. When OZ04 exactly equals OzA,
point C generates an arc of infinite radius, i.e., an exact straight line. By moving the
pivot Oz left or right from the position shown, changing only the length of link 1, this
mechanism will generate true circle arcs with radii much larger than the link lengths.