Pseudo-contact shifts (PCSs) can also be used to evaluate ensembles. The same averaging process as described above for the RDC is assumed. Hence correct structural superimposition is essential and one alignment tensor will be optimised for the entire ensemble.
One powerful feature of relax is that the paramagnetic centre can either be fixed or be allowed to move during optimisation. This allows an unknown paramagnetic centre position to be found. Or a known position to be refined to higher accuracy than that possible with most other techniques.