Automate Time & Date Insertion Upon Cell Selection

I have a Workbook with about 20 Worksheets, for each sheet I have a Selection Change Event that simply performs the Following:

MainSheet1. Range(“Z1”) = Now

1 Cell on every Sheet then is pointed to this cell via =Main!Z1. Problem is that when this is preformed Each Row from the Other In-Active Sheets and sometimes a near-by Button will Appear on my Active Sheet. I cannot select the parts of the sheets that appear and when I scroll down till they are out of view and then scroll back up they are gone until I select another cell and it happens again. I have tried in the Z1 cell to just put =NOW() and Make Calculations Manual and then with the selection change to call MainSheet1.Calculate or Workbook.Calculate but this has the very same effect and the other sheets bleed onto or ghost onto my Active Sheet. So far the only way I’ve been able to get around this is:

If Application. ScreenUpdating Then
Application.ScreenUpdating = False
MainSheet1.Range(“Z1”) = Now
Application.ScreenUpdating = True
Else
MainSheet1.Range(“Z1”) = Now
End If...............