Comment by manoDev | Hacker News Reader

Comment by manoDev | Hacker News Reader

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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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