Goldilocks and the Three Mobile Devices

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Once upon a time, there was a little girl named Goldilocks. She went for a walk in the forest. She was enjoying her walk and wanted to listen to some tunes. Her Motorola Xoom tablet was too clunky to switch songs easily, she didn’t even bring her iPod nano because it only had one button that frustrated her but her iPhone was just right. It was pocket-sized and she could easily switch songs. After a while she realized she was lost and wanted to see where she was in the forest in relation to the nearest shelter. While her iPhone did have maps it was too small and she could not see her surroundings very well. Her Xoom was very luxurious to look at a map on but she could do with something a bit more hand-held for the walk. Her Samsung Galaxy Tab was just right for seeing where she was and for carrying. Following the directions on the Tab, she came upon a house and knocked, let herself in and settled down for a quick read. Reading on her iPhone hurt her eyes, and though she had an eBook reader it was still too small for a long comfortable read. There was a rather large newspaper sitting on the table but the headline was a day old. Her Xoom tablet was just right for reading the story she had recently started; a story about 3 bears.

This modern, mobile fairy tale (she did have quite a few devices, didn’t she) posits that every use case and device has its own best scale or purpose. Considering it more deeply, while it’s true that every mobile device has its own set of specifications, the industry is settling on some roughly standard sizes expected for various form factors and uses. Mobile phones have a roughly 4.0″ screen size and a 480 x 800 screen resolution. While these metrics in physical dimenions are definitely trending upward, to stay mobile these devices will need to be able to still fit within a pocket to fit in this device category and be unconsciously mobile (something you bring with you everywhere without thinking about it). Another category of device that is exploding is the tablet device form factor. This label is being placed on devices that are both in the 10″ range and the 7″ range, which are seen as roughly the standard sizes for these devices. This does beg the question, when the term tablet is used, does it mean a 7″ device or 10″ device? We could create or classify a third category of devices that may absorb the 7″ tablet and that would be eBook readers like the Amazon Kindle or the Barnes & Noble Nook. Both of these devices measure in at around the 6-7″ range. While this is just labeling and there are literally an unlimited number of device sizes across the spectrum between these standards, it demands the essential point, “What is the purpose for what we are using the device?” That intended purpose will infer the the sizes and ideal metrics.

Simply put, how a person interacts with the device for how long and in what specific situation has a direct bearing on the form and scale of the device to be built and used.

But what about the user experience and the software that runs on the device? There are many apps out there that can be used for comparison of ideal size to utility. Using this information, we can see that how a device is used can drive what size is needed. Here are a few touch-points with real world equivalents.

Book:Probably the best comparison between mobile devices and their physical equivalent would be the book or other printed text such as a magazine or newspaper. This is made obvious by the single-use name of ‘eBook reader’ with one classification of size device listed above. While the eBook reader is convenient and lower cost than a full tablet, the typical paperback book starts at an “A Format” measuring 4.33″ x 7.01″ in size (8.2″ diagonal), coming out larger than the typical eBook reader. The “A Format” is the smallest of the typical dimensions and it gets larger from there: “B Format” at 5.12″ x 7.8″, “C Format” at 5.32″ x 8.51″, “Octavo” at 9″ x 6″, and the “Quarto” at 12″ x 9.5″ which is a 15.3″ diagonal (paperback sizes, hardback sizes). This actually makes a tablet class device a more accurate representation of its physical book counterpart. In general, successful eBook readers are about the same size as their real world printed counterparts.

Relative Book Cover Sizes

Relative Mobile Device Sizes

Map: Another use for mobile devices is an evolution from the standalone GPS devices and before that, paper road atlases. While a search for a pocket road atlas will come up with results from 5+ years ago measuring 6.2″ x 3.6″ (7.1″ diagonal) the modern paper road atlases come in midsized (10.5″ x 8.5″, 13.5″ diagonal) and deluxe (15.5″ x 11″, 19″ diagonal). Even the pocket size atlas does not match the modern pocket size device class but fits more closely to eBook reader or smaller tablet device. In spite of this key difference, it’s fair to say that the interactive map format has been “mobile-sized” pretty effectively via porting the UI and restructuring the user experience to more effectively take advantage of the smaller smartphone class device’s capabilities and work with the constraints.

Relative Road Atlas Sizes

Calculator: This is a precursor to our modern mobile devices and fits quite nicely into the pocket size device category not so much by virtue of emulation or replication of an object but by evolution. The typical pocket calculator matches the size of modern mobile pocket devices but the addition of scientific functions multiplies the size and moves it towards the larger class device categories. It only stands to reason that this new generation of pocket sized devices are capable and highly usable, but similarly proportioned grandchildren of the Texas Instruments classics of yore.

Music player: This comparison is also not emulation of an existing realworld device or object but an evolution of the medium that holds the music. From records, to tape devices to cd/discs and finally to our modern hard drive storage the devices have been shrinking based on ever improving technology and moving to the smallest possible usable device. Screens that are on these devices are there for controlling playback; that said… it may be going too far with nano-sized devices having too few controls. The smartphone sized UIs are highly usable, though they may have eschewed the iconic click wheel interface that drove so many music players during the first decade of the 2000′s.

Camera: Yet another device that has been shrinking based on lifting constraints rather than an optimal viewing size. Moving from the earliest box camera and toward the modern viewfinder cameras the viewing area has been shrinking and making the device more portable. Removing the requirements to house a canister of film also allowed for a lot of bulk to be shed. Just in the most recent decade, more view space has been added to LCD screens without compromising the portability of the device. This screen at an average 3″ diagonal matches the pocket size device class very well and continues to meet the needs of portability of the device. It’s no wonder that so many users are clamoring to get better cameras on their smartphones. The average Android-powered handset and the slim model point and shoots by Sony or Canon are not that far apart in terms of pocketability.

The first two physical world emulations have reason and utility to their size. A book can be looked at for long periods of time without strain because of small text (though good eyesight does help here!) and a map with the ability to compare distances across a large surface and being able to see entire routes makes the form factor a convenience. The last three examples noted above and many others use the available technology to make the view window and controls convenient and portable. This brings us back to the question of ideal metrics and scale for apps. While some apps have some size requirements for usability, apps generally tend to do better when they are customized solutions rather than trying to emulate other experiences that are familiar in the real world. As can be seen with the evolution of devices with various screen sizes, it is the best experience for the purpose and the device. So what apps utilize the screen the best and are the most successful?

A quick look at the iTunes store for top apps for both iPad and iPhone shows that games dominate the popular market right now. Honorable mention goes to other apps that are extensions of other media (Netflix, Pandora, Last.FM, Hulu), the iWork suite (Pages, Numbers, Keynote) and some social media extensions mostly for the pocket sized iPhone (Facebook, Twitter, Skype). Most of the non-game apps have an existing market on the desktop and are providing a continuation of service to the mobile device. They have taken user experience and the screen size into account in redesigning their experiences, but do not need to win solely on that at this point due to desktop use. Mobile games are in most cases solely available on the mobile device and have deeply considered screen size in most cases because they know where the app will be displayed and have built for that use case. This may also be why not many popular apps emulate physical objects (outside of Apple’s included Notes, Calendar, Calculator and other default apps). These apps are often limited by screens size and our expectations of use in the physical world. If the screen size matches our expectations of the real world parallel, we may see a popular app show up using skeuomorphic design but in either case accounting for screen size is crucial in developing for mobile. We believe at Float Learning that “mLearning is NOT eLearning courseware on a mobile device” and the best mobile experiences are customized for screen size.

Goldilocks has shown the bears and us that we do not live in a one-device world and that metaphoric user interfaces can only take us so far on certain size devices and in many cases can be the entirely wrong experience. Goldilocks knew she needed to find apps and mLearning that fit her context and her level of expectations as a user. One device that is “just-right” for one context with one app may not be when one of the variables changes.

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Erik is a Float Mobile Developer with a B.S. in Computer Science (University of Illinois Springfield) and Education (Illinois State University). Before working for Float, he created many community driven websites and online applications, as well as built interactive learning experiences. Erik has developed educational interactives for The Museum of Science and Industry, The Field Museum and The Adler Planetarium and has built and maintained customized content management systems for colleges, rapid eLearning companies, and real estate groups. Erik focuses on clean and creative development practices to build engaging experiences.



Erik's personal development blog is at

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On March 18, 2011
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