Should a keyboard layout optimize for hand alternation or for rolls?
Thanks to a really nice typing program called Amphetype, I have recently been able to collect some good data on my typing habits. I compiled some data and did a rudimentary analysis of my fastest and my slowest trigraphs. I analyzed my 180 fastest trigraphs and my 156 slowest trigraphs, classifying each one in one of three categories: fully alternating, alternating and rolling, or fully rolling. If it is fully alternating, then each key is typed on the opposite hand from the previous key. If it is fully rolling, then each key is typed on the same hand. And if the trigraph is alternating and rolling, then there are two consecutive keys on one hand, and the third key is on the other hand.
Among the fastest trigraphs, 10% were fully alternating, 75% were alternating and rolling, and 15% were fully rolling.
Among the slowest trigraphs, 21% were fully alternating, 38% were alternating and rolling, and 40% were fully rolling.
So what does this mean? First, let us remember that there are twice as many ways for a trigraph to be alternating and rolling as to be fully alternating or fully rolling. So given a random sample, we would expect a distribution of 25%, 50%, and 25%. The data I have isn’t totally accurate, but it should be pretty close. What’s clear from this data is that fully alternating keys and fully rolling are rarely very fast. Not only that, but you have to count down to the 13th fastest trigraph before you find one that isn’t alternating and rolling. So alternating and rolling is clearly the fastest possibility.
Now let’s look at the slowest trigraphs. These are more evenly distributed. But notice that there are not as many alternating and rolling trigraphs as you’d expect, and there are a lot more trigraphs that are fully rolling. So there are a lot of very slow trigraphs that are fully rolling.
As simple as this data may be, it still gives us some useful information. To optimize our keyboard, we should try to maximize combos where you type two keys on one hand and then switch to the other hand. Getting a computer to do this in practice, though, is tricky. My program is designed to use digraphs; it can use trigraphs with a small modification, but using trigraphs is orders of magnitude slower. We still may be willing to sacrifice speed for accuracy; but is there any way to still maximize our goal of two-keys-at-a-time using digraphs and not trigraphs? I certainly don’t see any way.