Grafana Gauge starting at fix date to now

Configuration Frontend
1

I want to create a Grafana Gauge for energy consumtion. The date ishould be the start date of the “energy supply contract”. The Gauge should show the whole consumption till now.

I Select for example the last 7 days
grafik

The queury is

SELECT difference(last("value")) FROM "sensor.zahlerstand" WHERE $timeFilter GROUP BY time($__interval) fill(null)

But the result is not correct like

grafik
grafik1484×385 19.9 KB

I tried as beginner so much, but I didn’t find the solution.

I need help.