Rhythm
There are two main competing philosophies about the best rhythm for a keyboard layout. In this context, “rhythm” refers to the pace at which typing moves from hand to hand.
Alternation
Section titled “Alternation”Dvorak was designed around alternation—that is, it states the ideal hand rhythm is that the left hand presses a key, then the right hand presses a key, then the left hand presses a key, and so on. For example, the quadgram data is an alternation on Dvorak:
Colemak, on the other hand, prefers rolls—each hand should press multiple keys before typing switches to the other hand. For example, the trigram oil is a roll on Colemak:
There is no universal agreement on which is better. According to Ec0vid’s Keyboard Layouts Doc, 3rd Edition:
Which to favor between rolling and alternation is subjective. It can be said that alternation offers a more consistent typing experience, as it feels rhythmic and minimizes awkward sequences. Meanwhile, rolling has higher highs (words that feel very smooth) but lower lows (long same hand sequences). Regardless, it is not a matter of one or the other. Think of it more as a scale, with max alternation on one end and max rolling on the other. We have to decide where on that scale we want our layout to be.
SFBs break rolls, meaning that any rolls within a same-hand sequence with an SFB must stop at the middle point of the SFB.
Roll Direction
Section titled “Roll Direction”There are two directions of rolls:
- In-roll: Towards the center columns, and
- Out-roll: Towards the far left or far right.
Many layouts from the 2010s assume that in-rolls is faster, more accurate, and more comfortable than out-rolls, so roll-heavy layouts from that era tend to have more in-rolls than out-rolls. This conventional wisdom has been challenged in the 2020s, with some saying that out-rolls should not be penalized. However, there is no universal consensus, and the preference or non-preference for in-rolls is now seen as a personal choice.
Redirect
Section titled “Redirect”A redirect, also called roll reversal or pinball in some older literature, is a same-hand sequence that changes direction—either from out to in, or in to out. Some people believe that redirects are uncomfortable and error-prone, though others see them as fine.
For example, on QWERTY, the trigram fad is a redirect:
Weak Redirect
Section titled “Weak Redirect”A weak redirect, also called bad redirect, is a redirect that does not involve the index finger or the thumbs. Most typists hold that because the middle, ring, and pinky fingers naturally move in concert with each other more so than the index and thumb, weak redirects are more difficult than other types of redirects. However, some typists have reported that muscle independence on the weak fingers can be built up with practice, making weak redirects comfortable for them.
On QWERTY, the trigram sad is a weak redirect, whereas fad (shown in the previous section) is not:
Thumb Redirect
Section titled “Thumb Redirect”A thumb redirect is a redirect that involves the thumb. On Maltron, the trigram sea is a thumb redirect, as is the trigram t o:
AKLDB excludes thumb redirects from total redirects because the thumbs have significantly more muscle independence than the other eight fingers.