While it is true that INS's exist, the cost of a reliable and accurate one is on the same order of magnitude as the CNC Machine itself. Also, errors accumulate

While it is true that INS's exist, the cost of a reliable and accurate one is on the same order of magnitude as the CNC Machine itself. Also, errors accumulate [0] over time in an INS (aka "Integration Drift"), such that it becomes wildly inaccurate after a certain critical threshold. Also, almost all INS's require regular calibration and tuning, [1] and are sensitive to vibrational stresses (which is abundantly present in a machine shop). Therefore it seems unlikely that these machines include INS's. [0] http://en.wikipedia.org/wiki/Inertial_navigation_system#Error http://en.wikipedia.org/wiki/Inertial_navigation_system#Erro... [1] http://www.aerostudents.com/files/avionics/navigationBasicsAndInertialNavigation.pdf http://www.aerostudents.com/files/avionics/navigationBasicsA... (scroll down to bottom for tuning discussion)