This work presents a re-analysis of published isotope-shift measurements in ytterbium optical clock transitions, with a focus on deviations from King-plot linearity. By comparing multiple transitions involving the 3Pj manifold, a clear state-dependent ordering of King-plot nonlinearities is identified. Transitions involving spin- and magnetically sensitive excited states exhibit systematically larger deviations from linearity than structurally simpler states. The analysis is based exclusively on existing experimental data and introduces no new parameters or fits. It highlights the role of internal-state structure and external-field sensitivity as key organizing principles for understanding King-plot deviations. Possible implications for field-dependent tests and precision clock spectroscopy are discussed, and the nonlinear regime is identified as a particularly sensitive window for probing internal atomic structure.
Jurgen Wollbold (Thu,) studied this question.