def __nuwalther(zed):
    """

    Calculate the kinematic viscosity for the Walther equation (ASTM D341).

    Parameters
    ----------
    zed: scalar
        The z-parameter of the Walther equation.

    Returns
    -------
    kin: scalar
        The kinematic viscosity.

    """
    kin = zed - 0.7 - 10 ** (-0.7487 - 3.295 * (zed - 0.7) + 0.6119 * (zed -
        0.7) ** 2 - 0.3193 * (zed - 0.7) ** 3)
    return kin
