Almost any computing application will have features you've never uncovered: That's why there are so many self-help computing books for dummies, or whatever publishers want to call users. However, some iOS apps offer completely different feature sets in portrait and landscape modes.
I noticed this in an interesting article about hidden iOS features on Macworld.com by staff writer Lex Friedman. He looked at features of the apps that ship with iOS, such as Clock, Calculator, Voice Memo and Weather.
He points out that the Calculator app in portrait mode presents an ordinary calculator, but becomes an HP-style scientific calculator when rotated to landscape mode. This is a very interesting interface.
Even with the crazy, anything-goes UI implementations accepted in Apple's iOS Human Interface Guidelines, this drastic functionality change between landscape and portrait modes seems to run counter to fundamental design concepts, such as user control.
People, not applications, should initiate and control actions. Although an application can suggest a course of action or warn about dangerous consequences, it’s usually a mistake for the app to take decision-making away from the user. The best apps find the correct balance between giving people the capabilities they need while helping them avoid dangerous outcomes.
Users feel more in control of an app when behaviors and controls are familiar and predictable. And, when actions are simple and straightforward, users can easily understand and remember them.
Yet, I understand how the designers consider that the rotation mode change is significant and could signal a switch in the program's capabilities. Apple's UI guidelines for the iPhone expect the programmers to let users see more and do more in landscape mode.
On iPhone, anticipate users’ needs when you respond to a change in device orientation. Users often rotate their devices to landscape orientation because they want to “see more.” If you respond by merely scaling up your content, you fail to meet users’ expectations. Instead, you should respond by rewrapping lines of text and, if necessary, rearranging the layout of the user interface so that more content fits on the screen.
I regularly use programs that reveal more information, tools or controls in landscape mode. I don't know that I love that change.
Interestingly, for the iPad, the interface suggestions are different.
Avoid gratuitous changes in layout. As much as possible, provide a consistent experience in all orientations. A comparable experience in all orientations allows people to maintain their usage patterns when they rotate the device. For example, if your iPad app displays images in a grid while in landscape, it’s not necessary to display the same information in a list while in portrait (although you might adjust the dimensions of the grid).
When possible, avoid reformatting information and rewrapping text on rotation. Strive to maintain a similar format in all orientations. Especially if people are reading text, it’s important to avoid causing them to lose their place when they rotate the device.
Still, to have an entire new calculator revealed in a rotation mode seems to me to be a stretch. Okay, a stretch that I will now take advantage of now that I know about it.