def saturation_correlate(M, Q):
    """
    Returns the *saturation* correlate :math:`s`.

    Parameters
    ----------
    M : numeric
        *Colourfulness* correlate :math:`M`.
    Q : numeric
        *Brightness* correlate :math:`C`.

    Returns
    -------
    numeric
        *Saturation* correlate :math:`s`.

    Examples
    --------
    >>> M = 0.108842175669
    >>> Q = 195.371325966
    >>> saturation_correlate(M, Q)  # doctest: +ELLIPSIS
    2.3603053...
    """

    s = 100 * (M / Q) ** 0.5
    return s