So, I have seen some people on the Internet showing the 738's PFD circular gauge for RA, but others show that the gauge is used for AOA(angle of attack). Which one is true? Is there a switch to change the circular PFD gauge between RA and AOA?
It’s a customer option (i.e. the operator can choose and specify) to switch between the two; presumably by pin programming the computer responsible for generating the display symbols.