Well, the value of QLcdNumber is set using the display() property. For the first time dealing with QLcdNumber shows a strange behavior.
Consider this example:
Qt Code: 
  1. void MainWindow::dataFromUdp(QByteArray pack)
  2. {
  3.     if(pack.at(0) == '!')
  4.     {
  5.         unsigned long x;
  6.  
  7.         x = (unsigned char)pack[pack.length() -1] +
  8.                 (unsigned char)pack[pack.length() -2] * 256 +
  9.                 (unsigned char)pack[pack.length() -3] * 256 * 256 +
  10.                 (unsigned char)pack[pack.length() -4] * 256 * 256 * 256;
  11.  
  12.         //extract packet
  13.  
  14.         if(x == crcCalculate(0, pack.length() - 4, pack))  
  15.         {
  16.             //CRC is correct
  17.  
  18.             if(pack[1] == 0x0d)
  19.             {
  20.                 number = 0;   // class member variable
  21.                 char value[6];
  22.                 sprintf(value,"%c%c%c%c%c", (char)pack[2],(char)pack[3],(char)pack[4],
  23.                         (char)pack[5],(char)pack[6]);  
  24.  
  25. //Now value = 00125
  26.  
  27.                 number = atoi(value)/1000.0;
  28.  
  29. //Now value is 0.125
  30.  
  31.                 ui->lcd_range->display(number);
  32.  
  33.                 qDebug() << number;
  34.  
  35. //Here number and qlcd are set to -3.6xx
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it's strange!