private string ParseResponse(byte[] buffer)
        {
            var pos    = 0;
            var header = Encoding.UTF8.GetString(buffer, pos, 4);

            buffer = buffer.Skip(5).ToArray();

            if (header == "RPOS") // Ignore other messages
            {
                RPOS rpos = ByteArrayToStructure <RPOS>(buffer);

                return(rpos.ToString());
            }
            return(null);
        }