
        >>> format_eng = EngFormatter(accuracy=1, use_eng_prefix=True)
        >>> format_eng(1_000_000)
        ' 1.0M'
        >>> format_eng = EngFormatter(accuracy=2, use_eng_prefix=False)
        >>> format_eng("-1e-6")
        '-1.00E-06'

        @param num: the value to represent
        @type num: either a numeric value or a string that can be converted to
                   a numeric value (as per decimal.Decimal constructor)

        @return: engineering formatted string
        rS