A mechanism which constrains the spatial location of a working or a focalpoint of a tool (103), has a manipulator (101) and a remote centre mechanism(102) mounted thereon. The manipulator (101) provides at least one degree offreedom for positioning the remote centre mechanism (102) which itselfprovides at least a further degree of freedom for positioning a tool holdersuitable for holding the tool (103) which is to be constrained in operationwith respect to a remote centre point. The orientation of the tool holder isadjustable whilst still maintaining the position of the remote centre pointfixed with respect to the manipulator (101).
