Create Stop Watch Application in ASP.Net example

Please refer below code.

HTML

<div>
    <asp:ScriptManager ID="Scriptmanager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:Label ID="Label1" runat="server" Font-Size="XX-Large"></asp:Label>
            <asp:Timer ID="tm1" Interval="1000" runat="server" OnTick="tm1_Tick" />
            <asp:Button ID="btnStart" Text="Start" runat="server" OnClick="Start" />
            <asp:Button ID="btnStop" Text="Stop" runat="server" OnClick="Stop" />
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="tm1" EventName="Tick" />
        </Triggers>
    </asp:UpdatePanel>
</div>

C#

public static Stopwatch sw;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        btnStop.Enabled = false;
        sw = new Stopwatch();
    }
}

protected void Start(object sender, EventArgs e)
{
    sw.Reset();
    sw.Start();
    btnStart.Enabled = false;
    btnStop.Enabled = true;
}

protected void Stop(object sender, EventArgs e)
{
    sw.Stop();
    btnStop.Enabled = false;
    btnStart.Enabled = true;
}

protected void tm1_Tick(object sender, EventArgs e)
{
    try
    {

        long sec = sw.Elapsed.Seconds;
        long min = sw.Elapsed.Minutes;
        if (min < 10)
            Label1.Text = "0" + min;
        else
            Label1.Text = min.ToString();
        Label1.Text += " : ";
        if (sec < 10)
            Label1.Text += "0" + sec;
        else
            Label1.Text += sec.ToString();

    }
    catch { };
}

Screenshot