Sensors　for　coordinate　measuring　machines　(CMM)　are　nowadays　assessed　within　a　measurement　system,　i.e.　while　mounted　onto　a　CMM.　This　means　that　the　accuracy　or　uncertainty　of　the　sensor　or　probe　is　not　really　identified　on　its　own,　but　may　be　influenced　by　the　accuracy　or　uncertainty　of　the　CMM　on　which　the　accuracy　testing　is　done.　Determining　the　accuracy　and　repeatability　of　a　sensor,　apart　from　the　machines　uncertainty,　could　yield　useful　information　in　several　cases.　For　instance　sensor　damage　can　be　ruled　out　after　a　machine　crash　if　the　sensor　could　be　tested　apart　from　the　machines　uncertainty.　Also　testing　a　new　sensor　on　an　older　machine　sometimes　poses　a　problem,　as　the　sensors　inaccuracy　can　vanish　in　the　total　uncertainty　of　the　measuring　system　due　to　a　high　CMM　uncertainty.　This　paper　describes　the　current　standardised　and　accepted　methods　for　evaluating　the　integration　of　a　CMM　sensor　in　the　environment　of　the　machine.　Furthermore　tests　are　described　to　exclude　the　CMM　uncertainty　as　best　as　possible　to　come　to　an　assessment　that　characterises　the　sole　sensor　uncertainty.　This　is　done　through　smart　positioning　of　the　reference　tool,　using　another　reference　tool　in　combination　with　another　measurement　strategy　or　using　extra　equipment　to　exclude　CMM　errors.　Preliminary　results　are　presented　and　discussed.