Track Changes
You can
keep track of each person who reviews this spreadsheet and when they
made their changes.
Each
reviewer's changes can be highlighted in a different color. If you
chose to Track Changes, you can see which changes were made, who
made the changes and where you can find their changes.
Try it:
Track Changes
Go to Review->Changes.
Select Track Changes.
As you review the tracked changes, you can choose to Accept
or Reject those changes.