There is a great deal to say about the interactions and interface, but let’s just take a moment to recount everything that the HUD does over the Iron Man movies and The Avengers. Keep in mind that just as there are many iterations of the suit, there can be many iterations of the HUD, but since it’s largely display software controlled by JARVIS, the functions can very easily move between exosuits.
Along the bottom of the HUD are some small gauges, which, though they change iconography across the properties, are consistently present.
For the most part they persist as tiny icons and thereby hard to read, but when the suit reboots in a high-altitude freefall, we get to see giant versions of them, and can read that they are:
In the 1st-person view we see that the HUD has a separate map in the lower-left, and object recognition/awareness,
Most of the HUD functions we see, though, are situational, brought up for Tony’s attention when JARVIS believes they are needed, or when Tony requests them. Following are screenshots that illustrate a moment when the situational function appeared.
Iron Man 2
Iron Man 3
Some of these illustrate why I argue that JARVIS is the superhero, and Tony just the onboard manager, but rather than reverse engineering any particular function, for this post it is enough to document them and note that only the optical zoom seems to be an interactive function. This raises questions of how he initiated the mode and how he escapes the mode, but since we don’t see the mechanisms of control, it’s entirely arguable that JARVIS is just being his usual helpful self again.