Left panel: flux ratio K_R in r band between SDSS and this work plotted as a function of g − r color of stars in the field. The 2016 data are plotted in red, while the 2015 data in blue, including some non-photometric measurements. These can be corrected using the 2016 fit by adjusting their K_R coefficient to the value derived from the 2016 fit computed at g − r = 0.8 using the vertical dashed line drawn at g − r = 0.8 which intersects the best fit relation of the 2016 data. Right panel: same for the K_Hα coefficient.