The variables of the first horn are:

Correspoinding the variables to those longitudes:

However in Valanis has other nomeclature, for now on we are using the Valanis nomeclature:

Where:

$$ \psi_e = psi_e = \arctan{\frac{(b_1 + b) / 2}{p_e}} \\ p_1 = \cos{\psi_e} \cdot \frac{b_1}{2} \\ \eta $$