container.css('opacity', '.5');
        refreshChart.count++;
        var seq = refreshChart.count;
        $.getJSON('?mode=plot&flags=' + mmuFlags())
         .fail(function(xhr, status, error) {
           alert('failed to load plot: ' + status);
         })
         .done(function(result) {
           if (refreshChart.count === seq)
             drawChart(result);
         });
      }