Scatter plot distribution of the velocity field values as measured by the remapped SO/PHI-HRT (x-axis) and SDO/HMI (y-axis) in the sunspot penumbra. The colors and lines are defined as in Fig. 3. The uncertainties represent one standard deviation estimated using the bootstrap method with 100 subsamples. The image in the lower right quadrant shows a snapshot of the sunspot observed by SDO/HMI oriented as in Fig. 1, and the blue contours define the penumbra boundaries.