The specs given reflect the supposed accuracy of the machine with the various probes specified. Any machine is no more accurate than its weakest link which is quite often the probe because people tend to think they can get any accuracy they want as long as there is a probe on the machine. If you need really great accuracy in measuring parts then the TP200 is the logical pick. If you need great accuracy in doing a lot of scanning then add the SP600. The TP20 and the TP2 are functionally the same probe but do provide a couple of microns less accuracy.