A CMM has no direct relation to a CNC.
In short, a CMM allows measuring in 3D all at once, at least all the probe tip can access. Depending on the system and software output the measurements in various ways. Simple xy measurements to a single origin, point to point on the part ect. Some can output point clouds for import into 3D software as a surface.
see http://en.wikipedia.org/wiki/Coordin...suring_machine as well.