var box_changed = new Array();

function clearBox(box) {
  if (!box_changed[box.name]) {
    box_changed[box.name] = box.value;
    box.value = '';
  }
}

function fillBox(box) {
	if (!box.value) {
    		box.value = box_changed[box.name];
    		box_changed[box.name] = '';
	}
}