private void Timer_Tick(object sender,EventArgs e)
{
        //lblTime.Content = DateTime.Now.ToLongTimeString();
        //lblTime.Content = DateTime.Now.ToString("HH:mm:ss:fff");

        //milliseconds++;
        //if (milliseconds >= 1000) {
        //    sec++;
        //    milliseconds = 0;
        //}
        //if (sec == 60) {
        //    min++;
        //    sec = 0;
        //}
        //lblTime.Content = string.Format("{0:00}:{1:00}:{2:D3}",min,sec,milliseconds);


        milliseconds += 15.560;

        if (milliseconds >= 1000) {
            milliseconds = 0;
            sec++;

            if (sec >= 60) {
                sec = 0;
                min++;
            }
        }

        lblTime.Content = min.ToString("00") + ":" + sec.ToString("00") + ":" +
            milliseconds.ToString("000").Substring(0,3);

        //lblTime.Content = String.Format("{0:00}:{1:00}:{2:000}", timer.Interval.Minutes, timer.Interval.Seconds, timer.Interval.Milliseconds);
    }

private void Start(object sender,EventArgs e)
        {
          timer.Interval = TimeSpan.FromMilliseconds(1);
          timer.Tick += Timer_Tick;
          timer.Start();
        }

public partial class MainWindow :Window
    {
        DispatcherTimer timer = new DispatcherTimer();

        int min = 0, sec = 0;
        double milliseconds = 0;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void Timer_Tick(object sender,EventArgs e)
        {
            //lblTime.Content = DateTime.Now.ToLongTimeString();
            //lblTime.Content = DateTime.Now.ToString("HH:mm:ss:fff");

            //milliseconds++;
            //if (milliseconds >= 1000) {
            //    sec++;
            //    milliseconds = 0;
            //}
            //if (sec == 60) {
            //    min++;
            //    sec = 0;
            //}
            //lblTime.Content = string.Format("{0:00}:{1:00}:{2:D3}",min,sec,milliseconds);


            milliseconds += 15.560;

            if (milliseconds >= 1000) {
                milliseconds = 0;
                sec++;

                if (sec >= 60) {
                    sec = 0;
                    min++;
                }
            }

            lblTime.Content = min.ToString("00") + ":" + sec.ToString("00") + ":" +
                milliseconds.ToString("000").Substring(0,3);

            //lblTime.Content = String.Format("{0:00}:{1:00}:{2:000}", timer.Interval.Minutes, timer.Interval.Seconds, timer.Interval.Milliseconds);
        }

        private void Start(object sender,EventArgs e)
        {
            timer.Interval = TimeSpan.FromMilliseconds(1);
            timer.Tick += Timer_Tick;
            timer.Start();
        }
    }

Stopwatch stopwatch = new Stopwatch();

    stopwatch.Start();
    for (; ;)
    {
        Console.WriteLine(stopwatch.Elapsed);
    }