Stop watch speed does not match with count variable using timer

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

namespace TestApplication
{
    public partial class TimerTest : Form
    {
        Stopwatch _stopwatch = new Stopwatch();
        System.Timers.Timer TTTimer = new System.Timers.Timer(1000);
        int timecount = 0;
        public TimerTest()
        {
            InitializeComponent();

        }

        private void Startbtn_Click(object sender, EventArgs e)
        {
          
            this.TTTimer.Interval = 1000; //1 sec
            this.TTTimer.Elapsed += new System.Timers.ElapsedEventHandler(TTTimer_Elapsed);
            this.TTTimer.Start();
           // _stopwatch.Start();
        }

        void TTTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            if (!_stopwatch.IsRunning)
                _stopwatch.Start();
            this.Invoke((Action)delegate()
            {
                label1.Text = _stopwatch.Elapsed.Hours + ":" 
                             + _stopwatch.Elapsed.Minutes + ":" 
                             + _stopwatch.Elapsed.Seconds
                             + " Count: " + timecount % 60; 
            });
            timecount = timecount + 1; //timecount++;
        }
        private void Stopbtn_Click(object sender, EventArgs e)
        {
            TTTimer.Stop();           
            _stopwatch.Stop();
            _stopwatch.Reset();

        }
    }
}