EXFO FastReporter 2 - Manual (Page 153)

Working with OTDR Files
Post Processing Software 143
Managing Markers
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If any event is present between two markers.
For example: In the below image, the blue lines indicate the position of
the marker for the new event which you are trying to add. Event 3 is
shown between these two markers. In this condition the application
displays an error message, to indicate that you cannot insert new
event.
Note: The manually modified events are displayed with an asterisk (*) mark. For
more information on changing display options, see Changing FastReporter
2 Options on page 25.