pic.line 画出来的为什么是一个个点呢

Private Sub DrawRealLine(picX As PictureBox, TimeCountX As Integer, DataFromComX As Integer, DataFromComLastX As Integer)

If TimeCountX - 1 > 0 And (TimeCountX - 1) * 15 < pic.Width Then
picX.Line ((TimeCountX - 1) * 15, DataFromComLastX * 70)-(TimeCountX * 15, DataFromComX * 70), vbBlue
End If
If (TimeCountX - 1) * 15 > pic.Width Then
TimeCount = 0
pic.Cls
End If

End Sub
这是画实时曲线的函数，理论上画出来的应该是线而不是点，但我画出来的却是一个个点，怎么回事呢？

附
Option Explicit

Dim DataFromCom As Integer
Dim DataFromComLast As Integer
Dim TimeCount As Integer


Private Sub Check1_Click()
If Check1.Value = 1 Then
MSComm1.InBufferSize = 1024
MSComm1.InBufferCount = 0
MSComm1.InputMode = 1
= 3
MSComm1.Settings = "9600,N,8,1"

Check2.Enabled = False

End If
If Check1.Value = 0 Then
Timer1.Enabled = False
Check2.Enabled = True

End If
End Sub

Private Sub Check2_Click()

If Check2.Value = 1 Then
MSComm1.InBufferSize = 1
MSComm1.InBufferCount = 0
MSComm1.InputMode = comInputModeText
= 2
MSComm1.Settings = "9600,N,8,1"

Check1.Enabled = False

End If
If Check2.Value = 0 Then
Timer1.Enabled = False
Check1.Enabled = True

End If
End Sub

Private Sub Command1_Click(Index As Integer)
'Timer1.Enabled = True
If MSComm1.PortOpen = False Then
MSComm1.PortOpen = True
End If
End Sub

Private Sub Command2_Click(Index As Integer)
Timer1.Enabled = False
MSComm1.PortOpen = False

End Sub

Private Sub Command3_Click()
Unload Form1
End Sub
Private Sub Form_Unload(Cancel As Integer)
    If MSComm1.PortOpen = True Then
    MSComm1.PortOpen = False
    End If
End Sub

Private Sub Form_Load()
Timer1.Interval = 1
Timer1.Enabled = False
PicScale pic

End Sub
Private Sub PicScale(picX As PictureBox)
picX.Scale (0, 8750)-(picX.ScaleWidth, -1400)
End Sub

Private Sub DrawRealLine(picX As PictureBox, TimeCountX As Integer, DataFromComX As Integer, DataFromComLastX As Integer)

If TimeCountX - 1 > 0 And (TimeCountX - 1) * 15 < pic.Width Then
picX.Line ((TimeCountX - 1) * 15, DataFromComLastX * 70)-(TimeCountX * 15, DataFromComX * 70), vbBlue
End If
If (TimeCountX - 1) * 15 > pic.Width Then
TimeCount = 0
pic.Cls
End If

End Sub

Private Sub MSComm1_OnComm()
Dim byte1() As Byte

Dim a As Byte
Dim b As Byte
Dim s As Integer
If MSComm1.InBufferCount > 0 Then
byte1 = MSComm1.Input

  a = byte1(0)
  b = byte1(1)
  s = a * 256 + b
  Text1.Text = s
  DataFromCom = Text1
  DataFromComLast = DataFromCom
  TimeCount = TimeCount + 1
  DrawRealLine pic, TimeCount, DataFromCom, DataFromComLast



End If
End Sub  这是整段编程