The ensemble of relaxation rates in the β-hairpin and adjacent loops were best described by an extended model-free spectral density function, with separate order parameters for fast and slow motions (𝑆 𝑓 2 , 𝑆 𝑠 2 ), confirming the presence of slower correlated motions within this structural unit. Despite the success of the combined high-and low-field approach, some discrepancies arose, particularly in the 𝑅 1 values at lower fields. These deviations were attributed to crossrelaxation due to the cross correlation of chemical shift anisotropy (CSA) and dipolar relaxation mechanisms in the absence of control of relaxation pathways during the relaxation period. This problem was later addressed in different ways by Ferrage and coworkers (see below).