Fig. 1 Schematics of the approach used to obtain model-free parameters for methyl groups in ubiquitin. A total of m methyl group CH RDCs are measured in i alignment conditions. The homogeneity of these alignment conditions is analyzed by SECONDA (Hus and Brüschweiler 2002; Hus et al. 2003). Since methyl groups undergo rapid axial reorientation (<fs) about the adjacent CC bond, RDCs are scaled down to the corresponding CCmet RDCs. For each alignment medium i, a tensor is obtained from HN RDCs using the SCRM approach (Lakomek et al. 2008a). The tensors are scaled to CC RDCs and combined into the F matrix, which is then inverted to solve the dynamically averaged spherical harmonics <Y2,M> for each residue. All reported order parameters represent the axial motion of the CC bond