CMM

http://en.wikipedia.org/wiki/Coordinate-measuring_machine

Discussion: http://forums.reprap.org/read.php?1,12918

• "Robot Arm Type": here a human guides a 'finger' of a device that looks like a robot arm over a model or sculpture. This deals well with overhangs and precise geometries like boreholes or outer diameters. Coordinate Measuring Machines, or CMMs are often built in this configuration.

http://en.wikipedia.org/wiki/Coordinate-measuring_machine

• "Generic Touch Probe": we can mount a touch probe toolhead on a 2+1 axis machine like a CNC router, mill, or RepRap. This is convenient if we don't have a robot arm handy.