Originally Posted by
galaxy flyer
I think the standard is the fuselage reference line—body angle. It was for the Global HUD.
Also, remember the US and the British reverse the meaning of Angie of Attack and Angke of Incidence. Lastly, AoA gauges don’t display angle but dimensionless units between zero and stall AoA.
Which is a good thing as Mach has a big effect on max AoA but you will stall* when you get to it.
*very loose term as you may well meet an intervention before stalling or AoA max.
CSeries in normal mode does a lovely job of maintaining a variable AoA limit if you just hold it at the Soft or Hard sidestick limit.
Many aircraft will push before you get too close.