def C_fingas(heavy, precent_dist_180):
    """
    Returns the constant C used in fingas model
    source : (Fingas, 2015)

    Parameters
    ----------
    heavy : True if the fuel need to follow a ln, else it will be a sqrt.
    precent_dist_180 : Percentage distilled by weight at 180 °C []


    """
    if heavy:
        return 0.165 * precent_dist_180
    else:
        return 0.0254 * precent_dist_180