Dependence of peak–peak amplitude (black squares) and slope (red triangles) of error signal on the strength of magnetic field. (a) F = 3 → F ′ = 4 of ⁸⁵Rb D₂ line. (b) F = 2 → F ′ = 3 of ⁸⁷Rb D₂ line. The insets show the dependence of capture range on the strength of magnetic field.