' Start drawing the graph.
Private Sub btnGraph_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnGraph.Click
    btnGraph.Text = "Stop"
    btnGraph.Refresh()

    DrawGraph()

    btnGraph.Text = "Start"
End Sub

' Draw a graph for 5 seconds.
Private Sub DrawGraph()
    ' Generate pseudo-random values.
    Dim y As Integer = m_Y
    Dim stop_time As Date = Now.AddSeconds(5)
    Do While Now < stop_time
        ' Generate the next value.
        NewValue()

        ' Plot the new value.
        PlotValue(y, m_Y)
        y = m_Y
    Loop
End Sub

' Generate the next value.
Private Sub NewValue()
    ' Delay a bit before calculating the value.
    Dim stop_time As Date = Now.AddMilliseconds(20)
    Do While Now < stop_time
    Loop

    ' Calculate the next value.
    Static rnd As New Random
    m_Y += rnd.Next(-4, 5)
    If m_Y < 0 Then m_Y = 0
    If m_Y >= picGraph.ClientSize.Height - 1 Then m_Y = _
        picGraph.ClientSize.Height - 1
End Sub

' Move the old data one pixel to the left. gr.DrawImage(picGraph.Image, -1, 0)

' Erase the right edge and draw guide lines. gr.DrawLine(Pens.Blue, wid - 1, 0, wid - 1, hgt - 1) For i As Integer = m_Ymid To picGraph.ClientSize.Height Step GRID_STEP gr.DrawLine(Pens.LightBlue, wid - 2, i, wid - 1, i) Next i For i As Integer = m_Ymid To 0 Step -GRID_STEP gr.DrawLine(Pens.LightBlue, wid - 2, i, wid - 1, i) Next i

' Plot a new pixel. gr.DrawLine(Pens.White, wid - 2, old_y, wid - 1, new_y)

' Display the result. picGraph.Image = bm picGraph.Refresh()

gr.Dispose() End Sub

Subroutine PlotValue uses the Graphics object's DrawImage
    ' method to move the current graph one pixel to the
    ' left. It then draws the new value.

Compare this example to Draw a continuous graph in a separate thread in VB .NET. This example uses a separate PlotValue subroutine rather than plotting values as they are generated because this better fits the model used by the other example.