So your saying if any cell value on the entire sheet is changed. You want a message box to popup displaying the value in that cell. Is this correct?
If any value in any cell on the entire sheet is manually change then have a Message Box Popup displaying the value in that cell.
This would mean if any value in all 1.5 million rows and 13,000 columns would be manually changed you want a Message Box to popup showing the value in that cell.