3x2x2: A New Method of Thumb Typing for Tablet Computers

Fast Company has an article 3 Ways the iPad Could Kill QWERTY. I find it unlikely that QWERTY as a typing construct is going to go away, as the system and the keyboards we know now have evolved over decades to its current refined state. See, for instance, this collection of early typewriter keyboards. However, I do think tablet PCs such as the iPad offer other possibilities for typing, especially given that typing on touchscreen tablets with traditional keyboards sucks. Touch typing is nearly impossible unless the tablet is laying flat on a surface, because you have to steady the device with one hand while typing with the other (while the now half-supported tablet shakes).

I’ve come up with two new typing methods optimized specifically for tablet PCs and how they are held. Typically, unless you are using a stylus, a tablet is held with two hands, with thumbs on the front or on the side of the device, and your four remaining fingers on the back. It’s a natural, grasping gesture for humans. This leads me to think there there could be two possible new typing methods: one typing using your fingers on the back of the device by making use of ghost fingers, and another typing with just your thumbs using the screen on the front of the device. I address Ghost Finger Typing in a separate post, but for now, let’s focus on thumb typing.

Thumb typing is, of course, not new. (Few things are.) Blackberry users have been typing with thumbs for nearly a decade now, and other mobile phone users have been texting using only thumbs prior to that. There even thumb keyboards, and several interesting designs for thumb typing on a touchscreen. I want to add one more: the 3x2x2 Method.

3x2x2 is based on what I feel are comfortable movements of human thumbs. This includes the angles they can move on the Y axis relative to the rest of the hand: ~70 degrees, ~45 degrees, and ~30 degrees. These three angles provide enough distance from each other that there can be some accuracy in adjusting the thumb’s position easily. Additionally, the thumb has two comfortable, usable states: extended straight out or flexed. (Thumbs can also curl under the palm, but for our purposes, that’s irrelevant, as you couldn’t use that on a tablet.) Other fingers probably have at least four potential states: extended, two curled states (that extra joint helps), and curled into the palm.

But for thumbs, we have three (3) angles (70/45/30) and two (2) usable states (extended/flexed). And you have two (2) thumbs. So 3x2x2.

This basic ergonometrics gives a possible 12 buttons (six for each hand) that can be easily used by a thumb while the rest of the hand is gripping the tablet. Twelve buttons aren’t enough for full keyboard, so I’ve gone back to the original texting method on mobile devices where groups of letters were mapped to a single key. Multiple taps on a single key cycle through the letters of that key until the user pauses or taps another key.

Of course, the buttons’ touch targets need to conform to the size of thumbs, which are on the large side of the average adult fingerpad (10-14mm). [For more on touch target size, I suggest reading Chapter 2 of my book Designing Gestural Interfaces or the source material "3-D Finite-Element Models of Human and Monkey Fingertips to Investigate the Mechanics of Tactile Sense,” (pdf) by Kiran Dandekar, Balasundar I. Raju, and Mandayam A. Srinivasan, The Touch Lab, MIT.]

Here’s what the keyboard looks like:

And here’s what it would look like on an iPad:

You’ll note the 3x2x2 is off-set slightly (~2 inches/8cm) from the bottom of the touchscreen to accommodate the tablet resting in the palm while typing. Because the height is only about 3 inches (7cm), it works equally well in portrait and landscape mode, even on smaller tablets.

Pressing the # sign will switch the keyboard to numbers, and from there, symbols can be accessed in a similar manner. Pressing and holding the Shift key would give you a Return.

I crudely prototyped this on the iPad using Adobe Ideas, and ran through several sample sentences. I found myself able to type moderately quickly, and certainly faster than I was able to hunt-and-peck type with one hand while steadying the iPad with the other hand.

The next step for this design would be to prototype it working on the iPad (or similar device), check its time against regular typing, and perhaps adjust which letters are associated with which keys. I replicated the alphabet groupings on traditional mobile phones and placed them in alphabetical order, but this put a number of important letters (E, S, R, A, O) on the left hand (not the dominant one for 90+% of the world), with the S being especially buried three letters down. I also have no idea how this would translate for other, larger, alphabets. But it was a fun experiment and, I think, a viable alternative to traditional keyboards for tablet computers.

Related Post: Ghost Fingers Typing for Tablet Devices

This was written by Dan Saffer. Posted on Tuesday, April 27, 2010, at 2:02 pm. Filed under Interaction Design, Product Concepts, Touchscreens. Bookmark the permalink. Follow comments here with the RSS feed. Post a comment or leave a trackback.