Rule #2

One thing that most designer forgets when it comes to mobile interfaces is how the complexity level should be different from a PC or Web application.
First of all, the screen is smaller. This is easily ignored when designing on a 22" pc monitor. Especially when it comes to very high resolution screens. I had way too many customer telling me how we should fit more on their device since it has much bigger resolution. Right... A 4" screen is a 4" inch screen, whatever resolution it has.
What's also different is how you interact with the mobile device in question. A PC experience is immersive. Your full and undivided attention is on the screen. Your desktop becomes a second home. You spend hours in front if it, IN your PC. On a mobile device it's very different. You focus on it for seconds or minutes at max. It's a small part of your field of view, and many times you're doing something else at the same time. Like driving a car. So the experience is by nature not immersive. You're not living in the screen. It's becoming a tool in your life. An indicator or a control panel of something.

So rule #2 is: no more than 7 things on a screen.

Things are defined as a button, a status, an icon indicating something, a map...
It's actually based on studies that people can recognize 7 things at a glance. If you put more on a screen, the user will have to scan through that screen multiple times to find what he's looking for.
Also based on studies, phones that have less button on them create an impression in potential buyers as being easier to use. Nokia used this finding and created a couple o phones where they joined up the buttons of the numeric pad into pairs. To make the device look like it has less buttons. (Well, it sure made those phones look STUPID and different, but not easier to handle. So trading buttons for confusion is not a great idea)
I actually beleive that 7 is a good median, but tge ideal number depends on country. Just take a look at consumer electronics in different countries. I've seen a DVR in Taiwan with over 50 buttons on the face of it. In Europe, you have typically around 7 buttons. In the US it's 1 or 2.
So this rule is not as strong and strict as rule #1 but it's just as important. A 4" screen with 20 clickable items shown on a screen is not a good idea.



-- Posted from my iPhone