Timer in VB.NET

Public Class Form1
    Private _elapseTimerRunning As Boolean = False
    Private _elapseStartTime As DateTime

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
        Timer1.Interval = 1000
        Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        txtTime.Text = Now.ToString("h:mm:ss tt")
        If _elapseTimerRunning = True Then
            Dim elapsedtime = DateTime.Now.Subtract(_elapseStartTime)
            txtElapsed.Text = String.Format("{0}hr : {1}min : {2}sec", elapsedtime.Hours, elapsedtime.Minutes, elapsedtime.Seconds)
        End If
    End Sub

    Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
        _elapseStartTime = DateTime.Now
        _elapseTimerRunning = True
    End Sub

    Private Sub btnStop_Click(sender As Object, e As EventArgs) Handles btnStop.Click
        _elapseTimerRunning = False
    End Sub
End Class