Maps of continuum intensity (a, b)) with marked penumbral boundaries 5P and 6P, respectively. The white arrows are analogous to those in Fig 1. Plots c, d) show the magnetic field strengths (top) and inclination (bottom) dependent on the position along the penumbral boundaries. The colours of symbols correspond to the position on the boundary. The small black symbols are the fits of the observed values with formulas written in the plots.