private void UpdateChart(object chart, Dictionary <string, DataContainer> dict)
        {
            Chart chart_ = (Chart)chart;

            // get all keys from the current connection
            var keys = dict.Keys.ToArray();

            // clear and update the graphs (for each key)
            foreach (string key in keys)
            {
                // if series does not exist, add it
                if (chart_.Series.IndexOf(key) == -1)
                {
                    Charting.AddChartSeries(this, key, chart_);
                }

                int i = dict[key].time.Length - 1;
                if (dict[key].time[i] != null)
                {
                    DateTime time = DateTime.ParseExact(dict[key].time[i], Constants.FMT, CultureInfo.InvariantCulture, DateTimeStyles.AssumeLocal);
                    chart_.Series[key].Points.AddXY(time.ToOADate(), Convert.ToDouble(dict[key].value[i]));
                }

                // remove old data points
                if (chart_.Series[key].Points.Count > Constants.n_datapoints_max)
                {
                    chart_.Series[key].Points.RemoveAt(0);
                }
            }
        }