def eta1_Vargaftik_and_Yargin_error(TK):
    """Estimated error in dynamic viscosity

    Parameters
    ----------
    TK
        K, temperature

    Returns
    -------
    Error in η, Pa s

    References
    ----------
    Vargaftik, N B, and V S Yargin.
    Ch 7.4: Thermal Conductivity and Viscosity of the Gaseous Phase.
    Handbook of Thermodynamic and Transport Properties of Alkali Metals,
    edited by R. W. Ohse, 45. Blackwell Scientific Publications, 1985.

    Notes
    -----
    "Errors in the viscosity and thermal conductivity factors for
    the lithium vapour atomic component, due to inaccuracy in
    calculating atom collision integrals, are equal on average
    to 3%, falling from 3.8% to 1.5% with increase of the temperature
    from 700 to 2500 K. The portion of the error which is determined
    by inaccuracy in establishing the value of $\beta^2_{12}$ is
    changed with the concentration of the molecular component, reaching
    its maximum at the saturation line. In the case of viscosity it is
    1 - 6 %, and for thermal conductivity it is 4 - 8 % (for T <= 2000 K)"
    """
    x1, y1 = (700, 3.8)
    x2, y2 = (2500, 1.5)
    return y1 + (y2 - y1) * (TK - x1) / (x2 - x1)