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