Residual dipolar couplings (RDCs) can be used to evaluate ensembles. The ensemble interconversion is assumed to be fast relative to timescale of the alignment process, hence a single tensor for all members of the ensemble will be used. As such, precise superimposition of structures using a logical frame of reference is very important. This can be performed in relax using the structure.superimpose user function. The RDCs can either be from external or internal alignment.