Use modeling aids
Cursor constraints and modeling aids assist in accurately locating objects in 3-D space.
The cursor can always move freely in space, but you will normally want to relate your modeling elements to the construction plane grid, existing objects, or coordinates in space.
Cursor constraints
There are two parts of the cursor: the cursor (1) and the marker (2). The cursor always follow the mouse movement.
The marker sometimes leaves the center of the cursor because of some constraint on it such as grid snap or ortho. The marker is a dynamic preview of the point that will be picked when the left mouse button is clicked.
When the marker is constrained, in elevator mode, for example, a tracking line (3) also displays.
Constraints move your marker to a specific point in space or make its movement track according to the constraint so you can model accurately.
Angle cursor constraint
Restrict the angle the cursor can travel.
Distance cursor constraint
Restrict the distance the cursor can travel.
Coordinate entry
Enter coordinates for cursor location.
Elevator mode (vertical cursor constraint
Specify a point that is a given distance above or below a point on the construction plane.
Tab key cursor direction lock
Lock the cursor direction with the Tab key.
Point filters
Extract individual x, y, and z coordinate values to create a new, composite coordinate.
Ortho
Restrict cursor movement to an angle.
Planar
Limit picking locations to an elevation.
Snap
Toggle the current snap mode state.
Modeling aids
CPlane
Set the construction plane in the active viewport.
DragMode
Specify the plane object dragging will be parallel to.
Nudge
Move objects a small increment using arrow keys.
Object snaps
Constrain the marker to an exact location on an object such as the center of a circle or the midpoint of a line.
SmartTrack
Turn on a system of temporary reference lines and points.