/* ---- validate Qty takes only numbers ---- */
function data_change(field)
     {
          var check = true;
          var value = field.value; //get characters
          //check that all characters are digits, ., -, or ""
          for(var i=0;i < field.value.length; ++i)
          {
               var new_key = value.charAt(i); //cycle through characters
               if(((new_key < "1") || (new_key > "9")) && 
                    !(new_key == ""))
               {
                    check = false;
                    break;
               }
          }
          //apply appropriate colour based on value
          if(!check)
          {
               field.style.backgroundColor = "Yellow";
			   alert ('Please fill in whole positive numbers only.');
			   field.value = "";
          }
		  else
		  {
			  field.style.backgroundColor = "white";
		  }
     }