Mathematical formula changes position

[Becker]

Hi again,
its hard for me to discribe my problem.
I get this from a modbus flex getter:

I want to make a easy formula:
Pverbrauch = Pgesamt - Pein + Pbezug
but the problem is the topic of Pges & Pein:

when I join them:

I get a array with topic "0" "1" and "2".

my formula:

but the topics a switching every day, for example sometimes "Pbez" is 0, sometimes 1, sometimes 2.
=> so the formula is wrong sometimes.

How can I get explicit topics for the values ?

[Becker]

sorry, I got my mistake after reading my own problem a few times

[Becker]

solution:
1.

define a topic

join as an object

getting defined values

correct formula

finish

[UnborN]

Hi Becker,

I'm glad you shared in detail the solution .. i was wondering where exactly the problem was

Its takes a little time to tweak it at the beginning (with debug nodes everywhere) but once you fully understand it, the join node is one of the most powerful nodes from the core nodes.