def SG_to_API(SG):
    """
    Return specific gravity of a liquid given its API, as shown in
    [1]_.

    .. math::
        \\text{API gravity} = \\frac{141.5}{\\text{SG}} - 131.5

    Parameters
    ----------
    SG : float
        Specific gravity of the fluid at 60 degrees Farenheight [-]

    Returns
    -------
    API : float
        API of the fluid [-]

    Notes
    -----
    Defined only at 60 degrees Fahrenheit.

    Examples
    --------
    >>> SG_to_API(0.7365)
    60.62491513917175

    References
    ----------
    .. [1] API Technical Data Book: General Properties & Characterization.
    American Petroleum Institute, 7E, 2005.
    
    """
    return 141.5 / SG - 131.5
