I am trying to generate what I thought would be a really simple plot of a device's state over time, in this case a heating element that turns on and off depending on the temperature. The plot should look like a square wave.
This question is coming up regularly, but finding the answer via a search engine is not really straightforward.
The solution is to generate numbers from the strings with a "Function", $fld[2]=~"on"?1:0.2 should work in your case.
Dont forget the correct Regexp, though.
To compound things, I can't even find where the .gplot file is stored!?!?!
Looks like you're on the beginning end of unix-expertship

Try to search for it with:
find /opt/fhem -name \*.gplot
or
grep -rl HeaterRelay /opt/fhem