SWR meter with second arduino



I was looking at this documentation for my information and I have a doubt about the connection.

Look at the comments..
So my question is, what’s the right connection?
On the original arduino (the one I call the master) or on the 2nd (the one I call the slave)?
Some body have build it?

Second question, it seemed to me to have seen that we could connect a 2nd Nextion with this second nano. (Example to display the swr only)
I can’t find this doc, unless I’ve revered?

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