Android Question 3 channel Bluetooth "oscilloscope" TOO slow

Sub Globals
    Private pnlP1, pnlP2, pnlP3 As Panel
    Private rctP1, rctP2, rctP3 As Rect
    Private cvsActivity, cvsGraph As Canvas
 End Sub

Sub Activity_Create(FirstTime As Boolean)
...
    cvsActivity.Initialize(Activity)    ' initialize the Canvas for the activity
...
    pnlP1.Initialize("pnlP1")
    Activity.AddView(pnlP1, 0, 14%y, 100%x, 28%y)
    cvsGraph.Initialize(pnlP1)
    rctP1.Initialize(0, 0, pnlP1.Width, pnlP1.Height)
    cvsGraph.drawRect(rctP1, Colors.Transparent, True, 0)
    pnlP1.Invalidate
...
End Sub

Public Sub MessageFromDevice(msg As String)
...
'Data held in three arrays P1data etc and position pointed to by P1x etc
            cvsGraph.Initialize(pnlP1)    ' initialize the Canvas for the panel
            cvsGraph.DrawLine(P1x-1, 150+P1data(P1x-1)/10, P1x, 150+P1data(P1x)/10, Colors.black, 1dip)
            pnlP1.Invalidate
            P1x = P1x+1
            If P1x > 1000 Then   'Clear screen
                cvsGraph.drawRect(rctP1, Colors.LightGray, True, 0)
                pnlP1.Invalidate
                P1x = 1
            End If
...
End Sub

Sub Globals
    Private pnlP1, pnlP2, pnlP3 As Panel
    Private rctP1, rctP2, rctP3 As Rect
    Private cvsActivity, cvsP1, cvsP2, cvsP3 As Canvas
...
End Sub

Sub Activity_Create(FirstTime As Boolean)
    ' Load the layout file
    Activity.LoadLayout("main")
    ' Initialize the Canvas for the activity
    cvsActivity.Initialize(Activity)

    ' Initialise the panel
    pnlP1.Initialize("")
    ' Add it to the Activity
    Activity.AddView(pnlP1, 0, 14%y, 100%x, 28%y)
    ' Initialise the panel on the canvas
    cvsP1.Initialize(pnlP1)
    rctP1.Initialize(0, 0, pnlP1.Width, pnlP1.Height)
... same again for P2 and P3
End Sub

Public Sub MessageFromDevice(msg As String)
...
        If hmsg ="P1 " Then
            P1data(P1x)=fmsg
            cvsP1.DrawLine(P1x-1, MP-P1data(P1x-1)/SF, P1x, MP-P1data(P1x)/SF, Colors.black, 1dip)
            P1x = P1x+1
            If P1x > pWidth-5 Then
                cvsP1.drawRect(rctP1, Colors.Transparent, True, 0)
                P1x = 1
            End If
        End If
... etc for P2 and P3
... not forgetting:
        Activity.Invalidate

End Sub