Hi,
Not sure this is what you're asking for but for the ISA deviation, take the Temperature given and the Flight Level, lets say -45°c and FL350
What you do is this:
Surface T° is 15°c decreasing 2°/1000ft, ISA T° at FL350 is therefore 35x2=70° - 15°= -55°c
So in this example we are ISA +10°c.
For NAM/NGM:
NAM= TAS*(NGM/GS), just remember that NAM/TAS=NGM/GS
There is also NGM = NAM +/- [(Wind speed*Time)/60]
Voilà
I hope this is what you asked for
J