Positional sensitivity profiles of specific (panel a) and non-specific (panel c) hybridization before (t = 0, thick curves) and after (t = 17, thin dashed curves) washing: The respective nucleotide-letters are given in the figure. The respective sensitivity terms estimate the mean contribution of the selected nucleotide at the given position to the observed intensity-increment with respect to the set-mean of the intensity (log-scale, see Eq. (41)). The two panels below (b and d) show the difference profiles 'washed-unwashed'. In addition to the single-base terms we also show nearest-neighbor (NN) terms of selected homo-couples (dotted curves, the original NN-profiles in the upper panels are omitted for clarity). The difference profiles estimate the mean relative stability of the respective nucleotide-letter at the given position against washing. Note that sequence position k = 1 faces towards the bulk solution whereas position k = 25 is attached to the chip-surface.