mouse clicking

Hi,
I'm a student and i am doing a project on Visual Basic 6 which connect to a slider. I have 4 buttons-Home,Left,Right and Exit. if i click on Home button the slider(actuator)will move to the original place which is position 0. when i click on the Left button, the slider will move to position 200.when i click left button again, the slider will move from position 200 to 220, but the slider did not move to position 220, so how can i made the slider move to the position when i press the 2nd times
this is my program....... pls help.........

Private Sub cmdexit_Click()
End
     
End Sub

Private Sub cmdhome_Click()

outslider$ = "!99HOM0130@@" & Chr$(13) & Chr$(10)
If MSComm1.PortOpen Then
       MSComm1.Output = outslider
       End If
       Text1.Text = outslider$
cmdhome.Enabled = True
cmdleft.Enabled = True
cmdright.Enabled = True
cmdexit.Enabled = True
End Sub

Private Sub cmdleft_Click()
outslider$ = "!99PMV010   00300001@@" & Chr$(13) & Chr$(10)

If MSComm1.PortOpen Then
       MSComm1.Output = outslider$
        End If
    Text1.Text = outslider$
End Sub



Private Sub Form_Load()
cmdhome.Enabled = True
cmdleft.Enabled = False
cmdright.Enabled = False
cmdexit.Enabled = True

  MSComm1.CommPort = 1                 'Set COM1
  MSComm1.Settings = "9600,N,8,1"      ' Settings: 9600 baud, no parity, 8 data bits, 1 stop bit
  MSComm1.PortOpen = True              ' Open the port with the settings above
 
End Sub

Private Sub Form_Unload(Cancel As Integer)
 MSComm1.PortOpen = False             ' Close the port (let other programs use it)
End Sub