def kappa(A: float, B: float, C: float):
    """
    Calculate Ray's asymmetry parameter for a given set of A, B, and C rotational constants.
    This parameter determines how asymmetric a molecule is by setting a range between two limits: the prolate (+1)
    and the oblate (-1) limits.

    Parameters
    ----------
    A, B, C: float
        Rotational constant in MHz for each respective axis

    Returns
    -------
    kappa: float
        Ray's asymmetry parameter
    """
    return (2 * B - A - C) / (A - C)