AutoCAD 2008 User's
Guide > Create and Modify
Objects > Use Precision
Tools > Restrict Cursor
Movement >
Use Orthogonal Locking (Ortho Mode)
You can restrict cursor movement to horizontal and vertical for convenience and precision when creating and modifying objects.
As you create or move objects, you can use Ortho mode to restrict the cursor to the horizontal or vertical axis. As you move the cursor, the rubber-band line follows the horizontal or vertical axis, whichever is nearest the cursor.
The orientation of the current user coordinate system (UCS) determines the horizontal and vertical directions. In 3D views, Ortho mode additionally restricts the cursor to the up and down directions. In that case, the tooltip displays a +Z or -Z for the angle.
You can turn Ortho on and off at any time during drawing and editing. Ortho is ignored when you enter coordinates or specify an object snap. To turn Ortho on or off temporarily, hold down the temporary override key, SHIFT. While you use the temporary override key, the direct distance entry method is not available.
For drawing or editing objects at angles that are not parallel to the horizontal or vertical axis, see Use Polar Tracking and PolarSnap.
If turned on, the isometric snap setting takes priority over the UCS in determining horizontal and vertical directions.
