A residual RV shift vector map across different echelle orders is shown here. The possible residual shift in each exposure is calculated by measuring the centroid of a set of lines in each exposure (Fig. 2). The calculated shift in each line (0.0001 times length of the red arrow) with respect to the centroid of the corresponding line in the first exposure (black dot). The centre wavelength of each order is considered to be zero. The y-axis represents the order number in Keck/HIRES CCD2. Also, the centre wavelength of each order is mentioned on the right side of the plot.