Event.add(document, 'ready', function(e)
{
  var _inpt = DOM.$('calc_kr'),
      //_btn = DOM.$('calc_submit'), // The button is just for show, you see...
      _res = [
        {
          elm    : DOM.$('calc_res_classic'),
          ppm : 10
        },
        {
          elm    : DOM.$('calc_res_premium'),
          ppm : 15
        }
      ];


  if (_inpt)
  {
    var _lastVal = '',
        _metakeys = [
           8, // backspace
          46, // del
          13, // enter
          37, // left-arrow
          39, // right-arrow
           9  // tab
        ];

    // cancel non-number inputs
    Event.add(_inpt, 'keypress', function(e){
      var _key = e.which;
      if ((_key < 48 || 57 < _key) && Array.indexOf(_metakeys, _key) == -1) { return false; }
    });


    // recalculate
    Event.add(_inpt, 'keyup', function(e){
      var _val = this.value;
      if (_val != _lastVal)
      {
        _lastVal = _val;
        Array.forEach(_res, function(res){
          if (res.elm)
          {
            res.elm.innerHTML = Math.round(_val.toInt()*(res.ppm/1000));
          }
        });
      }
    }); 

    Event.fire(_inpt, 'keyup');

  }


});