Imports System.Windows.Forms.DataVisualization.Charting
...
Private random As New Random()
Private pointIndex As Integer = 0
...
Private Sub timerRealTimeData_Tick(sender As Object, e As System.EventArgs)
   ' Define some variables
   Dim numberOfPointsInChart As Integer = 200
   Dim numberOfPointsAfterRemoval As Integer = 150
 
   ' Simulate adding new data points
   Dim numberOfPointsAddedMin As Integer = 5
   Dim numberOfPointsAddedMax As Integer = 10
   Dim pointNumber As Integer
   For pointNumber = 0 To _
      (random.Next(numberOfPointsAddedMin, numberOfPointsAddedMax)) - 1
      chart1.Series(0).Points.AddXY(pointIndex + 1, random.Next(1000, 5000))
   Next pointNumber
 
   ' Adjust Y & X axis scale
   chart1.ResetAutoValues()
 
   ' Keep a constant number of points by removing them from the left
   While chart1.Series(0).Points.Count > numberOfPointsInChart
      ' Remove data points on the left side
      While chart1.Series(0).Points.Count > numberOfPointsAfterRemoval
         chart1.Series(0).Points.RemoveAt(0)
      End While
 
      ' Adjust X axis scale
      chart1.ChartAreas("Default").AxisX.Minimum = _
       pointIndex - numberOfPointsAfterRemoval
      chart1.ChartAreas("Default").AxisX.Maximum = _
      chart1.ChartAreas("Default").AxisX.Minimum + numberOfPointsInChart
   End While
 
   ' Invalidate chart
   chart1.Invalidate()
End Sub 'timerRealTimeData_Tick