def size_GB(xr_object):
    """
    How many GB (or GiB) is your xarray object?
    
    // Requires an xarray object
        
    // Returns:
    * equivalent GB (GBytes) - 10^9 conversion
    * equivalent GiB (GiBytes) - 2^ 30 conversion
        
    < Thomas Moore - thomas.moore@csiro.au - 10102018 >
    """
    bytes = xr_object.nbytes
    Ten2the9 = 10 ** 9
    Two2the30 = 2 ** 30
    GBytes = bytes / Ten2the9
    GiBytes = bytes / Two2the30
    print(xr_object.name, 'is', GBytes, 'GB', 'which is', GiBytes, 'GiB')
    return GBytes, GiBytes
