Fig. 11.
From: Evaluation of candidate geomagnetic field models for IGRF-11
Left plot shows differences 
in units nT/yr defined in (1) between SV 2010–2015 candidate models and the mean model M as a function of the index of the spherical harmonic coefficient (running from 
etc indexed 1, 2, 3, 4, 5, etc). Right plot shows Huber robust weighting factor
i
w
α
(1.0 full weight, 0.0 zero weight) also as a function of the index of the spherical harmonic coefficient.