How To Create A Stop Watch In C#

using System.Diagnostics;

Stopwatch st = new Stopwatch();
      private void btnStart_Click(object sender, EventArgs e)
      {
          timer1.Start();
          st.Start();
          label2.Text ="Start Time : "+ DateTime.Now.ToLongTimeString();
      }

      private void btnStop_Click(object sender, EventArgs e)
      {
          timer1.Stop();
          TimeSpan ts = st.Elapsed;
          label1.Text = "Duration : " + ts.ToString();
          st.Stop();
          label3.Text = "End Time : " + DateTime.Now.ToLongTimeString();
      }

      private void timer1_Tick(object sender, EventArgs e)
      {
          label4.Text = DateTime.Now.ToLongTimeString();
      }