Sky flat field analysis for the F160W filter. Left panel: absolute sky flat field measured for the June 2009 to July 2013 period, using the datasets corresponding to the proposal IDs listed in Table 1. Right panel: ratio of our sky flat field for the F160W to its corresponding MAST SD flat field uc721145i. Notice the different colour scale, spanning only a ∼1% for the flat field ratio panel. The right panel was smoothed with a 3 pixel wide Gaussian kernel to enhance the differences between different regions.