Minimum number of receptors needed to detect a 1° change in angle as a function of disorder. The number is calculated according to equation (2.7) using the averaged recombination rates shown in figure 2 for the respective membrane (M) and cytosolic (C) radical pair models. Orange line, 1-0 RP-M; yellow line, 1-0 RP-C; green line, 2-0 RP-M; blue line, 2-0 RP-C; purple line, 1-1 RP-M; red line, 1-1 RP-C.