E-mailed daily report network summary is different than network summary on Untangle

Why does our e-mailed network summary differ from the amount shown on the Untangle itself for the same day. E-mailed report shows network usage of 2.7 gigabytes and 86281 sessions passed. Network Summary on UT shows 3.3 gigabytes and 100472 sessions passed for the same time. See screenshots

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I have also attached the report settings. Can someone help me out?

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