Synthesised fitted line profile (black line) against the observations from the Hamburg atlas (points). Grey points were cut from the initial fit; blue points show areas where the deviation between initial fit and data is too high, and so the subsequent fits do not use the offending points; red points are used for computing all fitted quantities. Removing the points on right hand side removes the strong blend, and sigma-clipping handles weaker ones during fitting. w_K is the width of the broadening kernel used. Note that this line is not used in the final determination of the silicon abundance because of the large line blends.