Excel Code Question (simple)

hello.
is anyone familiar with coding in excel?
I want to calc sum of 1 cell

__A_B_C_D
1_X_Y_Z_sum
2

X,Y FROM DDE SERVER
Z= X/Y

I want to get sum of z.value and locate this value on "D1"

I googled and found follow code

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$C$1" Then
[D1] = [D1] + Target
End If
End Sub

but I heard that this code makes excel slow
So what is simplest code to calc this value??

Thanks

 

Use VBA setlinkondata() to run a macro when DDE X or Y change.

Code:

sub ddeupdate() 
range("c1") = range("a1")+range("b1")
range("d1") = range("d1") + range("c1")
end sub

sub start_links()
ActiveWorkbook.SetLinkOnData "DDE_X_Link", "ddeupdate"
ActiveWorkbook.SetLinkOnData "DDE_Y_Link", "ddeupdate"
end sub()

sub stop_links()
ActiveWorkbook.SetLinkOnData "DDE_X_Link", ""
ActiveWorkbook.SetLinkOnData "DDE_Y_Link", ""
end sub()

Simple loop filtering DDE bid and ask links

Code:

Sub Start_update_bid_ask
Dim aLinks As Variant
    Dim i As Long
    aLinks = ActiveWorkbook.LinkSources(xlOLELinks)
       If Not IsEmpty(aLinks) Then
          For i = 1 To UBound(aLinks)
           If UCase(Right(aLinks(i), 4)) = "?ASK" Or Case(Right(aLinks(i), 4)) = "?BID"  Then
           ActiveWorkbook.SetLinkOnData aLinks(i), "Call Update Macro" 
           End If
          Next i
       End If