@classmethod
def _parse_value(cls, stream_rdr, offset, value_count, value_offset):
    """
        Return the rational (numerator / denominator) value at *value_offset*
        in *stream_rdr* as a floating-point number. Only supports single
        values at present.
        """
    if value_count == 1:
        numerator = stream_rdr.read_long(value_offset)
        denominator = stream_rdr.read_long(value_offset, 4)
        return numerator / denominator
    else:
        return 'Multi-value Rational NOT IMPLEMENTED'
