Randy, they are extremely accurate measuring machines that usually have a gantry and a granite base. They are typically used to measure 3 dimensional coordinates in things like plastic molded parts or machined parts where they must be accurately measured to ten thousandths of an inch. This is used to trend quality control and processes. If on a plastic part, a certain critical dimension is too long, they could fine adjust the cooling cycle and control that dimension. On complex machined parts like a car engine, they can measure very exactly whether surfaces ar perpendicular to each other and machined concentrically and things like that. Here's a picture of one. The probe at the end is what touches the part, and that is where the ruby balls that are made so accurately are used.
http://www.brownandsharpe.com/cmm_microhite_3d_reflex.asp