Software Design Lessons from my Diving Computer

As I started my new hobby diving, I was told that the first gear should be an individual mask because it would contain prescriptive lenses. Well, why having a mask when you could have a new computer?? So, I invested in a Suunto Vyper dive computer.
Obviously, it is ruggedized and has touch points that can be operated with gloves and under water. But no touchscreen, no colorful display, only a few, very basic animations. Still, there is a more or less complex algorithm running inside. While playing around with it, I found some interesting aspects.
User interface is about simplicity. Suunto uses a menu working with up/down and a select buttons. When a sub-menu is selected, it shows that you are now a level deeper in the menu tree but it keeps showing the parent menu name. Idea is to ensure you where you are. If you have understood this strategy, you are fine. Besides diving, no more functions. Everything is focused. For me, this reflects a philosophy which apps should follow: Being focused on their task.
The UI needs to work in its environment. The UI of the computer is a simple LCD which can be illuminated in the dark. Because of the LCD, there cannot be two different things in the same place if the computer is in different status. You always know where to expect what. If you go deeper in water, you lose colors down to the point where only blue is left. Without an active light source, colors play no role. Therefore, a LCD black and white display is fine. Think about the environment in which your app is used. How much of what makes sense when? Colors and strengths of ambient light, think about it. Sound and vibration, think about it.
UI should mean user guidance. One thing I am missing (and here a richer display would be a great help) is user guidance. The computer expects you to be an expert. It comes with secure defaults, so normally nothing should go wrong. But whenever you change the percentage of oxygen for a Nitrox dive, it asks you about the partial pressure of oxygen you would like to go for (the secure default is 1.4 bar). I am pretty sure that most people diving in the summer then storing the gear for the rest of the year will need a short guidance to remember the details. Here, additional interface power and the opportunity to get a short lesson would be nice.

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