a breakaway unit sits atop a base plate of a coordinate measuring machine via a breakaway coupling system . a crash detection system including at least one crash detection sensor mounted on the breakaway unit and a crash detection controller stops the machine when vertical movement of the breakaway unit exceeds a threshold . should collision occur , the breakaway coupling system allows the breakaway unit to separate from the base plate , preventing damage to instruments mounted thereon . the kinematic coupling system preferably comprises tooling balls engaging respective vee cones , vee grooves , and / or flats .