Re: the timezone / 4 hour offset, see the latter part of this thread.
For the calculation (current feed-in number - feed-in number the day before at 23:59), let’s rewrite as:
t1 - t2
Does this code return the correct value?
import "experimental/date/boundaries"
day = boundaries.yesterday()
t1 = from(bucket: "Stromzähler")
|> range(start: -1m)
|> filter(fn: (r) => r["_measurement"] == "Einspeisung")
|> filter(fn: (r) => r["_field"] == "value")
|> last()
t2 = from(bucket: "Stromzähler")
|> range(start: day.start, stop: day.stop)
|> filter(fn: (r) => r["_measurement"] == "Einspeisung")
|> filter(fn: (r) => r["_field"] == "value")
|> last()
result = join(tables: {t1: t1, t2: t2}, on: ["_time"])
|> map(fn: (r) => ({_value: (r._value_t1 - r._value_t2)}))
|> yield(name: "t1_minus_t2")
