difference in data values

[rjobaan]

yesterday I made export to csv

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	Energy Used Wh	Usage_2
11-12-2015 12:45	5882	312
11-12-2015 12:50	5905	276
11-12-2015 12:55	5930	300
11-12-2015 13:00	5955	300
11-12-2015 13:05	5981	312

My Energy used was lik this
And this morning

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	Energy Used Wh	Usage_2
11-12-2015 12:45	5901	312
11-12-2015 12:50	5924	276
11-12-2015 12:55	5949	300
11-12-2015 13:00	5974	300
11-12-2015 13:05	6000	312

How can there be a difference. USage_1 is both cases 0 and usage_2 is the same?
I don't understand