Upper panel: comparisons of the abundance ratios, [X/Fe], as a function of the atomic number ( Z), for BS 16920–017 (filled circles and triangles) and HD 4306 (open circles and triangles). The circles indicate abundances derived from neutral species and triangles indicate those from ionized species (for Ti, V, Cr, and Fe). The dashed line is a reference at [X/Fe] = 0.0. Lower panel: abundance differences, on the logarithmic scale, between the two stars. The dashed line indicates the average of the values of the α elements (Mg, Si, and Ca).