def density_to_API(rho15):
    """
    Return the API from the density

    Parameters
    ----------
    rho15 : Density at 15°C [kg/m³]

    """
    d = rho15 / 999.06      #cf https://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html?vA=15&units=C#
    return (141.5/d) - 131.5