Introduction to 3D Design - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 3

Absolute coordinates
The location of all entities in AutoCAD is related to a coordinate system. Any coordin-
ate system is characterized by an origin and positive directions for the X and Y axes.
The Z axis is obtained directly from the X and Y axes by the right-hand rule: if we
rotate the right hand from the X axis to the Y axis, the thumb indicates the positive Z
direction.
Picture that when prompting for a point; besides specifying it in the drawing area with
a pointing device such as a mouse, we can enter coordinates using the keyboard.
The format for the absolute Cartesian coordinates related to the origin is defined by
the values of the three orthogonal coordinates, namely, X, Y, and Z, separated by
commas:
X coordinate, Y coordinate, Z coordinate
The Z coordinate can be omitted.
For instance, if we define a point with the absolute coordinates 30, 20, and 10, this
means 30 absolute is in the X direction, 20 is in the Y direction, and 10 is in the Z
direction.