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Note that if you chose to group by total or by collection point and selects two or more groups that contain the same measurement object (same id) the report will only count these measurement objects once, so the total row will show the actual number of events.
But if Group A contains Measurement object 1111 and Group B also contains Measurement object 1111 and a report is created grouped by Group or Measurement object the values for 1111 would be counted twice in the total row. Each row would show the actual values but the total row will show a value that has counted 1111 twice.
Read more about overlapping groups in the section groups.
Example of overlapping groups