Equivalent scale factor of the probe light intensity. The offset at I₀ = 1.02 mW is subtracted from all the signals. Dash dotted line with squares: K_{Ω − I0} = −104 °/h · mW⁻¹ at B_x = −2.3 nT (compensation point); Solid line with circles: K_Ω − I₀ = 0.03 °/h · mW⁻¹ at B_x = −5.7 nT (zero point); Dotted line with left triangles: K_Ω − I₀ = −57.4 °/h · mW⁻¹ at B_x = Ȓ3.9 nT (positive offset); Dashed line with right triangles: K_Ω − I₀ = 50.5 °/h · mW⁻¹ at B_x = −7.5 nT (negative offset). In our experiments, K_Ω − I₀ at zero point can be suppressed by above three orders compared with that at compensation point. The error bars of the experimental data are plotted along with the lines, but they are too small to be distinguished.