pert:
You can have two different sketches open at the same time with different boards selected if you start two instances of the Arduino IDE from the Arduino shortcut, by running arduino.exe, or by opening an .ino file associated with the Arduino IDE. Any other window opened from one of those instances (File > New, File > Open, File > Examples, File > Sketchbook) will reflect changes made to any other window that belongs to that instance.
Ok, many thanks, I tried that and it works. I had only tried opening another sketch from inside the IDE before.
Correlation, not causation.
fair enough.
I've never seen anything like that. Which Arduino folders do you mean? Which version of the Arduino IDE?
Aah! I have looked again and realised that not all of my sketch folders (in Documents>Ardunio) contain the 'debug' folder and the 'board.buildinfo' file. Only some, and these (I think) were all edited at some stage with VisualMicro. But the latest ones don't have it, so the latest version of VisualMicro doesn't do the same.
I'm glad I asked the question, some mysteries solved. And I can delete some rubbish. Thanks again.