Linear function (orange line) fit to the pB, B-measurements (black dots). Three panels represent the cases when the best-fitting parameter b provides an unbiased estimate of the F-corona intensity F (top left panel, C = 0), an overestimated value of F (top right panel, C > 0), and an underestimated value of F (bottom panel, C < 0). Since K ≥ pB, no (pB, B)-point can appear within the gray shaded area below the line B = pB + F with a slope equal to 1.