Altimeter in cockpit
Also known as an altitude meter, it's used to show the height above sea level. The cockpit currently offers a "height-above-elevation" meter, which is great for landing, but not really useful when you are 5+ km above the ground.
Altitude, on the other hand, represents the atmospheric density, and thus how strong the jet engines can run at a given height. If I'm in a jet plane, I'd like to know how effective my jets are as I maneuver around a mountain. It also comes standard with flying in about every instance possible, so its absence feels out of place to me.
The current meter doesn't need to be scrapped or anything, and the current flight interface doesn't need to be cluttered with extra widgets. I imagine the altitude can just be superimposed on the altitude indicator that already sits in the bottom-right (see picture for example).
Thanks for reading.