VB picture控件显示实时波形求教

我的程序是上位机发送1下位机返回1通道的数据，现在是上位机发送1下位机能返回1通道的数据，上位机的text也可以显示出数值。但是这个picture显示有点问题。下位机传上来几个数值如3.30V、3.24V、0.78V 等 。这个picture显示每个电压都有好几个点，应该是一个电压一个点的。 显示程序如下，图片在压缩文件中
Private Sub MSComm1_OnComm()
Dim t As String
Dim t_x(40), t_y(40) As Integer
Dim tt_y(40) As String


t = MSComm1.Input

For i = 0 To 39 Step 1

    t_x(i) = i * (Picture1.Width / 50)

Next i
For i = 0 To 39 Step 1
      t_y(i) = Picture1.Height - Val(Mid(t, i + 1, 1)) * (Picture1.Height / 25)
      tt_y(i) = Mid(t, i + 1, 1)
Next i
If flag = 1 Then
        Picture1.Cls
          For i = 0 To Picture1.Width Step 100
        Picture1.Line (i, 0)-(i, Picture1.Height), &HFFC0C0
    Next i
       For i = 0 To Picture1.Height Step 100
        Picture1.Line (0, i)-(Picture1.Width, i), &HFFC0C0
    Next i
For i = 0 To 39 Step 1
       Picture1.Circle (t_x(i), t_y(i)), 20
         Text2.Text = Text2.Text & tt_y(i)
       Next i   
End If
If flag = 2 Then
          Picture2.Cls
             For i = 0 To Picture2.Width Step 100
        Picture2.Line (i, 0)-(i, Picture2.Height), &HFFC0C0
    Next i
      For i = 0 To Picture2.Height Step 100
        Picture2.Line (0, i)-(Picture2.Width, i), &HFFC0C0
    Next i
   For i = 0 To 39 Step 1
       Picture2.Circle (t_x(i), t_y(i)), 20
         Text3.Text = Text3.Text & tt_y(i)
   Next i
   End If
If flag = 3 Then
          Picture3.Cls
             For i = 0 To Picture3.Width Step 100
        Picture3.Line (i, 0)-(i, Picture3.Height), &HFFC0C0
    Next i
     For i = 0 To Picture3.Height Step 100
        Picture3.Line (0, i)-(Picture3.Width, i), &HFFC0C0
    Next i
   For i = 0 To 39 Step 1
       Picture3.Circle (t_x(i), t_y(i)), 20
         Text4.Text = Text4.Text & tt_y(i)
   Next i
   End If
If flag = 4 Then
        Picture4.Cls
            For i = 0 To Picture4.Width Step 100
        Picture4.Line (i, 0)-(i, Picture4.Height), &HFFC0C0
    Next i
     For i = 0 To Picture4.Height Step 100
        Picture4.Line (0, i)-(Picture4.Width, i), &HFFC0C0
    Next i
   For i = 0 To 39 Step 1
       Picture4.Circle (t_x(i), t_y(i)), 20
         Text5.Text = Text5.Text & tt_y(i)
   Next i
End If