Demo of Timer

Design

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows.Forms;

    namespace Watch
    {
        public partial class Form1 : Form
        {
            int a, b, c;,
            public Form1()
            {
                InitializeComponent();
            }
            private void timer1_Tick(object sender, EventArgs e)
            {
                if(c>100)
                {
                    b++;
                    c = 0;
                }
                if (b>60)
                {
                    a++;
                    b = 0;
                }
                c++;

                label1.Text = a.ToString();
                label2.Text = b.ToString();
                label3.Text = c.ToString();
            }
            private void button1_Click(object sender, EventArgs e)
            {
                timer1.Enabled = true;
            }
            private void button2_Click(object sender, EventArgs e)
            {
                timer1.Enabled = false;
            }
            private void button3_Click(object sender, EventArgs e)
            {
                a = b = c = 0;
            }
            private void button4_Click(object sender, EventArgs e)
            {
                listBox1.Items.Add(label1.Text + ":" + label2.Text + ":" + label3.Text);
            }
            private void button5_Click(object sender, EventArgs e)
            {
                listBox1.Items.Remove(listBox1.Text);
            }
        }
    }
                

Output