Whenever you or a colleague changes an item, the change log is updated and a new revision is created. If you click on the history button on an item you can see the history dialog.

A dialog will be shown with all versions on a time line. You can select one or more version to see the

version number,
the action (like add, edit, delete, undelete, etc.),
the name of the user who changed it,
the date and time of the change,
the change comment

If you have two or more selected the differences between the selected versions will be indicated by a red arrow and section title:

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