function openPopUpWindow(htmlFile, windowName, windowHeight, windowWidth)
  {
   // Open a popup window function.

   // Define the number of parameters passed to the JavaScript function.
   var numberOfParameters = openPopUpWindow.arguments.length;

   // Define the new window's name, height and width. 
   var New_Window_Name, New_Window_Height, New_Window_Width;

   if (numberOfParameters == 1 || numberOfParameters == 2 || numberOfParameters == 4)
      {
       if (numberOfParameters == 1)
	  {
           // If the window’s name, height and width parameters are omitted (null), default the
           // new window’s name, height and width.
      	   New_Window_Name   = "popup";	
       	   New_Window_Height =  260;
       	   New_Window_Width  =  600;
	  }
       else
	  {	
       	   if (numberOfParameters == 2)
	      {	
	       // If the window’s height and width parameters are omitted (null), default the
	       // new window’s height and width.
      	       New_Window_Name   = windowName;	
       	       New_Window_Height = 260;
       	       New_Window_Width  = 600;
	      }
       	   else
	      {	
      	       New_Window_Name   = windowName;	
       	       New_Window_Height = windowHeight;
       	       New_Window_Width  = windowWidth;
	      }
	  }

       // Define the new window's height, width, status, reliability, toolbar usage, menu
       // bar usage, and scrollbars usage.
       var windowString = "height=" + New_Window_Height + ",width=" + New_Window_Width +
			  ",status=yes,resizable=no,toolbar=no,menubar=no,scrollbars=yes";

       // Center the popup's window for opening.
       if (window.screen)
          {
	   var yc = ((screen.availHeight - 30) - New_Window_Height) / 2;
           var xc = ((screen.availWidth  - 10) - New_Window_Width)  / 2;
           windowString += ",left = " + xc + ",screenX=" + xc;
           windowString += ",top = "  + yc + ",screenY=" + yc;
	  }

       // Open Popup window.
       window.open(htmlFile, New_Window_Name, windowString);
      }
  }