StopWatch? iN C#? I encountered a problem!

Question

As the subject, I am making a StopWatch. You know, to learn Timer!

Ok, here's my code: (ms = 1, hour, min, second = 0)

    private void timerDisplay_Tick(object sender, EventArgs e)

        {

            ms++;

            if (ms == 10)

               {

                   sec++;

                   ms = 1;

               }

            txtMilisecond.Text = "." + ms;

            if (sec == 60)

               {

                   min++;

                   sec = 0;

               }

           txtSecond.Text = "" + sec;

           if (min == 60)

              {

                   hour++;

                   min = 0;

              }

              txtMinute.Text = "" + min;

              txtHour.Text = "" + hour;

        }

When I run this, it gets faster and faster than an usal watch!

Anyone knows the problem?

Thanks,