Break a single contour into two contours. The break will occur at one or two set points. To set a point, first select the current point then select the Set 1 or Set 2 button.
If only one set point is set, then the original contour will contain all the points before the set point, and a new contour will contain the set point and all the points after the set point. This is usually what you want for breaking open contours but is much less useful for breaking closed contours.
If both points are set, the second contour will contain points between and including the two set points and the first contour will contain the remaining points. This is usually the best way to obtain the desired break with a closed contour.
Use Unset to undefine the second point and use only a single point for breaking.
If Use current point for 1 is selected, then the current model point will automatically be used for set point 1.
The hot key Ctrl+B can be used in any window to break the contour, as long as this dialog is open.