Response functions of the Ca I 4227 Å line, calculated in the FAL-C atmospheric model for an LOS with μ = 0.1. The upper four panels show, clockwise from the upper left, the RF for the Stokes parameters I, V, U, and Q, accounting for all MO effects. The bottom four panels show the RF for the same Stokes parameters, artificially setting the ρ_V coefficients to zero in the RT calculations from which the RF is computed.