The Sa button provide a way of toggling the on/off status of the and Snap commands. With Snap On, Objects will be forced to line up with the SNAP Grid. Note that the Snap Gird and the Display Grid (Gd) can be different.
Point snapping is a function used to place an object relative to another drawn object with greater precision than when manually selecting the location and drawing the object.
Point snapping is used as follows:
1. Click one of the Point Snap Fields (Sa).
2. Select a drawing command from the Draw menu. Point snapping can be used on a line, Polyline, circle, or an arc.
3. Click the object in the drawing to which the new object is to be snapped.
4. Complete the drawing according to the prompts on the status bar.
The newly drawn object snaps to the snap grid.