Ah! Yes! Oh wow I love this! Many years ago, back when everyone was just discovering smartphones (we used to call them smartphone back then, now we just call t

Ah! Yes! Oh wow I love this! Many years ago, back when everyone was just discovering smartphones (we used to call them smartphone back then, now we just call them phones...) and figuring out that widgets need to be larger in order to be easier to touch, I was having a beer with a colleague who was doing design back at the time and we were making an inventory of all the ways that this is going to change things. And we thought this was going to be one of them, and we had the math to prove it! Fitts' famous law considers all axes of motion equal -- i.e. it's a model that describes moving horizontally, diagonally, horizontally or anything in-between as equally difficult. This isn't the case for phones, especially not when they're used with a single hand. Horizontal motion at the bottom of the screen is very hard, because your thumb just don't bend that way. So is vertical motion on the right-hand side of the screen (for right-handed users -- left-hand side for left-handed users). Diagonal motion is easier because, well, that's how the thumb bends. It's not just about the difficulty of making the motion happen -- the motion is inherently imprecise (this is what Fitts' law effectively cares about, not necessarily the amount of physical effort). We tried to sketch a "revised" model but it was a little unwieldy to plug into the beautifully-logarithmic Fitts equation. I think I still have that notebook. Unfortunately, we never pursued it further. I'm a lowly programmer and not really interested in UX design anymore. My colleague was so burned out by academia that he didn't want to touch anything even vaguely resembling a research project with a ten-foot pole and I didn't even dare suggest publishing something 'cause I sort of valued our friendship. However, it's something that's been lurking in the community for a while. I've mentioned it every once in a while, and almost every time I've heard something along the lines of "huh, I think I've seen this, too, I wonder if we could make a useful UI like this". Turns out you can and it's finally happening!