Utility meter wrong? Differs from source sensor!


I created some utility meters to display average heat amount of my heat pump per day, per week, per month and per year.

Now I am a little bit confused, because they seem to give me wrong values.

For example during last week:
original sensor (total_heat_amount) counted 255.6 kWh per week, while the utility meter total_heat_amount_weekly counted 271.2 kWh per Week.

What’s going wrong here? Is this difference occurring because of roundups while counting?

Here is a picture of the slowly rising difference: