def C_venturi_nozzle(D, Do):
    """Calculates the coefficient of discharge of an Venturi style nozzle 
    used for measuring flow rate of fluid, based on the geometry of the nozzle.
    
    .. math::
        C = 0.9858 - 0.196\\beta^{4.5}
        
    Parameters
    ----------
    D : float
        Upstream internal pipe diameter, [m]
    Do : float
        Diameter of nozzle orifice at flow conditions, [m]
        
    Returns
    -------
    C : float
        Coefficient of discharge of the nozzle orifice, [-]

    Notes
    -----
    
    Examples
    --------
    >>> C_venturi_nozzle(D=0.07391, Do=0.0422)
    0.9698996454169576
    
    References
    ----------
    .. [1] American Society of Mechanical Engineers. Mfc-3M-2004 Measurement 
       Of Fluid Flow In Pipes Using Orifice, Nozzle, And Venturi. ASME, 2001.
    .. [2] ISO 5167-3:2003 - Measurement of Fluid Flow by Means of Pressure 
       Differential Devices Inserted in Circular Cross-Section Conduits Running
       Full -- Part 3: Nozzles and Venturi Nozzles.
    """
    beta = Do / D
    return 0.9858 - 0.198 * beta ** 4.5
