Draw a grid in picturebox1

PublicClass Form1' Size of picturebox1 is 315;102 !!!!!!!!!!!!!!PrivateSub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) HandlesMyBase.Load

    Randomize()
    m_OldValue = 0

    Dim bm AsNew Bitmap(PictureBox1.Width, PictureBox1.Height)Dim gr As Graphics = Graphics.FromImage(bm)

    gr.DrawLine(Pens.Black, 0, 101, PictureBox1.Width, 101)

    gr.DrawLine(Pens.Black, 0, PictureBox1.Height, 0, 0)


    For j AsInteger = 0 To 300 Step 10
      gr.DrawLine(Pens.Black, j, PictureBox1.Height, j, 98)Next jFor j AsInteger = 0 To 300 Step 20
      gr.DrawLine(Pens.Black, j, PictureBox1.Height, j, 95)Next jFor i AsInteger = 10 To 80 Step 10
      gr.DrawLine(Pens.Black, 0, i, 4, i)Next iFor i AsInteger = 20 To 80 Step 20
      gr.DrawLine(Pens.Black, 0, i, 7, i)Next iFor j AsInteger = 20 To 300 Step 20
      gr.DrawLine(Pens.Cyan, j, 94, j, 0)Next jFor i AsInteger = 20 To 80 Step 20
      gr.DrawLine(Pens.Cyan, 4, i, PictureBox1.Width, i)Next i

    PictureBox1.Image = bm

  EndSubPrivateConst m_Dx AsSingle = 3Private m_OldValue AsSinglePrivateFunction NewValue() AsSingleDim new_value AsSingle

    new_value = m_OldValue + Rnd() * 8 - 4
    If new_value > 99 Then new_value = 99If new_value < 1 Then new_value = 1
    NewValue = new_valueEndFunctionPrivateSub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.TickDim bm AsNew Bitmap(picturebox1.Width, picturebox1.Height)Dim gr As Graphics = Graphics.FromImage(bm)
    gr.DrawImage(picturebox1.Image, +m_Dx, 0)

    gr.DrawLine(Pens.Black, 0, 101, PictureBox1.Width, 101) 'plot horizontal black line

    gr.DrawLine(Pens.Black, 0, PictureBox1.Height, 0, 0) 'plot vertical line but wrong !!!


    gr.ScaleTransform(1, -101 / picturebox1.Height)
    gr.TranslateTransform(0, -101)

    For i AsInteger = 20 To 80 Step 20
      gr.DrawLine(Pens.Cyan, 0, i, PictureBox1.Width - m_Dx, i)Next iDim new_value AsInteger = NewValue()
    gr.DrawLine(Pens.Red, 0 + 1 + m_Dx, m_OldValue, 0 + 1, new_value)
    m_OldValue = new_value

    picturebox1.Image = bm

  EndSub