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Comment by manoDev | Hacker News Reader

> I'd argue that modal behavior isn't a bad thing so long as those modes are very clearly distinguished.

No, that's bad. Your user can always miss the cues, in fact, you have to design considering they will miss.

In vim and other examples you gave, modes aren't a problem less because the distinction is clear and more because being in the wrong mode is not a cause of disaster - but they're still annoying.

The problem with the Airbus VS would exist regardless of indication of the mode it's in, even if it had a giant bright orange screen explaining the value shown is in feet not degrees, because the operator would develop blindness to it. A possible solution is having two VS displays, one for feet and another for degrees, such that the operator can disambiguate at a glance. Another is standardizing to one unit only (which is harder).

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One display, clearly labeled with a different color, different font, using degree symbols vs. "ft/s" units - you're saying this is bad, but two displays right next to each other, labeled similarly, isn't?

A display like this...

    [ ] Mode [10.0000 DEG]

...that once toggled turns into this...

    [X] Mode [32.1234 FTS]

... is bad. This is better:

    [10.0 DEG] [32.1234 FTS]

You don't have to think, you can use different decimal places to reinforce cues, you can confirm the values are correct by seeing both values at a glance. Further, there's no mode button to fault, the display can't be in an inconsistent state (accusing one mode and showing the value of another).

Sometimes you can use modes to hide unnecessary information, but for something that answers the question how fast am I falling you really don't want ambiguity or cognitive load.

Barring all other problems, there's no cognitive overhead when it's clearly labeled. You simply read what it says.

There is [1] if the user is used to it showing something and it's showing another. This is the core problem with modes.

What people have to understand is that it doesn't matter how clearly you think you're labeling it, if it breaks the user expectation, it's not clear at all - and an experienced user reads even less, which is the case of a pilot.

Once the pilot develops an habit of, e.g., switching the vertical speed display from feet/s to degrees during final approach (and that may have been what happened), and one day he forgets to switch, or the mode button malfunctions, or double clicks by mistake... there you have a recipe for disaster.

[1] http://en.wikipedia.org/wiki/Inattentional_blindness

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