To edit an existing element in Arc mode

Select Insert Element.
Select Arc from the Mode option menu.
Specify the portion of the element to be changed by entering two data points.
The former line string is removed and a double rubber band is attached to both points specified. The solid rubber band tells where new arcs are to be defined.
Enter two data points to define one arc.
The arc will be defined by the first point entered in step 3 and the two points entered in step 4.

If you press Reset after one data point, step 4 is started again.

After one arc is defined, a dashed rubber band displays between the end of the arc and the second point specified in step 3.
A line is drawn between the end of the last arc and the point where the dashed rubber band was connected. The modified element is then placed as a complex chain.