private short makeChecksum(Object d) {
		short checksum = 0;
		String data = d.toString();
		byte[] dataBytes = data.getBytes();
		
		for (int i = 0; i < dataBytes.length; i++) {
			checksum += (short) dataBytes[i];
		}
		while ( checksum / 0xff != 0) {
			checksum = (short) (checksum & 0xff + checksum >> 8);
		}
		checksum = (short) ~checksum;
		
		return checksum;
	}