Formula

Jtandme 

Based on your description, assuming you have two sheets called "Tracking" and "Invoice" and if you want to copy the cell A13 on Invoice Sheet if changed to the first empty cell after the last row with data in column A on Tracking Sheet, place the following code on the Invoice Sheet Module.

To do so, right click on Invoice Sheet Tab --> View Code and paste the code given below into the opened code window and save your workbook as Macro-Enabled Workbook.

If name of your tracking sheet is not "Tracking", change the name of tracking sheet it in the code.

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.CountLarge > 1 Then Exit Sub
Dim wsDest  As Worksheet

Set wsDest = Worksheets("Tracking")     'Assuming Tracking is the name of the Tracking Sheet, change it as required

If Target.Address(0, 0) = "A13" Then
    If Target <> "" Then
        Target.Copy wsDest.Range("A" & Rows.Count).End(3)(2)
    End If
End If
End Sub

Let me know if this is what you were trying to achieve.