def _compute_term1(self, C, mag):
        """
        Compute magnitude dependent terms (2nd and 3rd) in equation 3
        page 46.
        """
        mag_diff = mag - 6

        return C['c2'] * mag_diff + C['c3'] * mag_diff ** 2
Compute magnitude dependent terms (2nd and 3rd) in equation 3
        page 46.