To facilitate the selection of Sets near the center of the stereonet, the Add Set Window (Circular) option can be used.
To add a circular Set window:
Select Add Set Circular from the Sets menu.
Move the cursor over the stereonet in the active view, and you will see a circular Set Window appear, which follows the cursor.
When the circle encloses the desired data, click the left mouse button, and you will see the Add Set Window (Circular) dialog.
The Add Set Window dialog for a circular Set Window is similar to the Add Set Window dialog for the curvilinear Set Windows, except that only a single orientation is required, the Plunge or Dip angle which defines the circle radius. The center of the window is always fixed at the center of the stereonet (i.e. Trend / Plunge = 0 / 90) and cannot be edited by the user.
For the purpose of creating Sets in Dips, a circular set window is identical in all respects to a curvilinear four-sided set window. All of the same rules regarding sets and set windows apply. See the Add Set Window topic for more information.