Relative distortion residuals. Top: point source trace on the detector was extracted from PID 1050, and the distortion solution from Wells et al. (2015), and this work was used to transform the iso-α trace into α, λ coordinates. Since the point source should have a fixed spatial coordinate, this illustrates the improvement in the distortion model using the flight data. The residual modulation originates from the under-sampling of the MRS PSF. Bottom: distribution of iso-α residuals for all dither point of PID 1049 and PID 1050, obtained by applying the distortion transforms derived in this work.