Autodesk in 2003 received a US patent on the RevCloud command's ability to draw a redline shape made of arcs. The patent describes a method of determining the arc's size by the first arc drawn while the mouse button or Shift key is depressed:
the bulge spacing function comprises setting the bulge spacing for the multiple arc segments equal to the bulge spacing of a first arc segment when:
* a first point of the first arc segment has been selected;
* an arc defining key has been depressed and held down; and
* a second point of the first arc segment is selected.