Average relative minimum errors in the measured energy-integrated Stokes q and u as a function of observation time for the one-spot models (calculated as ΔS/S = ([Δq/q_m]_min + [Δu/u_m]_min)/2. The solid blue curve shows the errors with the fiducial parameters (shown in Table 1). The blue dash-dotted curve corresponds to similar data but with p_max = 0.1171, the black dashed curve with i = 50°, the black dash-dotted curve with i = 70°, the red dashed curve with θ = 10°, the red dash-dotted curve with θ = 30°, and the orange solid curve with ρ = 30° (also explained in Table 2). Curves were interpolated from the calculated points as in Fig. 6.