Why do Contact Center Analytics entered intervals not add up to total entered sum?

Contact Center Analytics was built to help capture ongoing transactions and is done through the Entered Column.

The formula for calculating what is in the entered column is: Entered = Accepted + Diverted + Total Abandoned + Waiting in Queue.

So because of this adding up the individual slots (i.e. if split by 15 mins, 30 mins or 1 hour) it will not match the total sum of Entered in the summary section for all queues.

So as an example: Although X Company rarely gets calls on holidays they have someone online to cover them if they come in.  On one such holiday agent Robin was working.  During Robin's day one call came in at 7:20 and another came in at 7:28.  Robin finished the first call at 7:31 and then took the second call.  When Robin's supervisor looked at the reports for that day they saw 2 entered for the period between 7:00 and 7:30 and 1 entered for the period between 7:30 and 8:00.  So the total of entered for the periods would be 3 even though only 2 came in.