Plot allowing determination of the rotation velocity of the primary (x-axis) when the equilibrium state is reached () for various values of the surface magnetic field (y-axis). The relations between these two quantities are given by the lines. For example, the rotation of the primary in a system composed of a 10 and a 7 M_⊙ star (blue continuous lines) when the orbital period is 1.1 days, assuming the primary has a surface magnetic field of 10 kG, would be around 137 km s^-1. The blue continuous lines are for a mass ratio q = M₂/M₁ = 0.7 and the red dashed lines are for a mass ratio q = 0.2.