Examples of the calibration of the Dopplergrams measured by SDO/HMI for AR 12489. (a): average LOS velocities estimated in the quiet-Sun at disk center as a proxy for the observatory velocity, (dotted gray line). The black line is the obtained by Eq. (1). (b): solar differential rotation obtained from Eqs. (2)–(4), shown with black lines, for the lower-left (dotted line), middle (solid line), and top-right (dashed line) pixels inside a FoV with a size of 310″  ×  185″. The green line is the average LOS velocity of the adjacent quiet-Sun. (c): convective blueshift estimated using Eq. (5) at the same three pixels inside the FoV, shown with black lines, with the μ values given by the blue lines.