We also need what goes along with HUDs : switches, nubs, switches, dials. Actual controls.

Although we are talking HUDs, I'm not really talking about UI widgets having the good old skew-morphism or better buttons. In the cockpit the pilot doesn't have his controls on a touch screen, he has an array of buttons and dials and switches all around him. It's these controls that are used in response to what the pilot sees on the HUD and it's these controls that change the aircraft according to the pilots will, which in turn change what the HUD shows.