Scissors

A scissor is when a finger extends to the far side of the keyboard at the same time as an adjacent longer finger flexes to the near side.

Note

In anatomical terms, a scissor is the simultaneous opposing flexion-extension of adjacent fingers, where the shorter finger extends while the longer finger flexes.

In colloquial use, scissors refer to a wide variety of motions that are considered uncomfortable, including some that do not fit the definition above. However, there is significant disagreement on which scissors are considered “bad.” The proportions of finger lengths vary from person to person as does each person’s ability to move each finger independently of the others.

Some examples of common scissors on QWERTY include:

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Scissor Bigram

A scissor bigram is a bigram that creates a scissor motion between adjacent fingers. Scissors are classified by distance:

• Half-scissor bigram (HSB): 1u distance between the two keys
• Full-scissor bigram (FSB): 2u distance between the two keys

$\text{HSB}\% = \frac{\text{\# of half-scissor bigrams}}{\text{\# of bigrams}}$

$\text{FSB}\% = \frac{\text{\# of full-scissor bigrams}}{\text{\# of bigrams}}$

$\text{Total Scissor}\% = \text{HSB}\% + \text{FSB}\%$

Scissors are considered uncomfortable due to the opposing motion of adjacent fingers, which can strain the tendons and reduce typing fluidity. Modern layouts often optimize to minimize scissors, though there is significant individual variation in scissor tolerance.

Note

Extended scissors (3u+) are theoretically possible but rare in standard typing due to corpus sanitization excluding numbers and most symbols.

Finger Pair Classification

Different finger pairs have varying degrees of independence, affecting scissor severity:

• Index-middle scissors: Generally most tolerable due to higher finger independence
• Middle-ring scissors: Moderate severity
• Ring-pinky scissors: Generally least tolerable due to lower finger independence

Scissor Skipgram

A scissor skipgram is a skipgram that creates a scissor motion between adjacent fingers. Like bigrams, these are classified by distance:

• Half-scissor skipgram (HSS): 1u distance between the two keys
• Full-scissor skipgram (FSS): 2u distance between the two keys

$\text{HSS}_1\% = \frac{\text{\# of 1st order half-scissor skipgrams}}{\text{\# of trigrams}}$

$\text{FSS}_1\% = \frac{\text{\# of 1st order full-scissor skipgrams}}{\text{\# of trigrams}}$

Scissor skipgrams capture uncomfortable patterns where the scissor motion happens with an intervening keypress, such as “c_r” in “car”. While less severe than direct scissors, they can still impact typing comfort and rhythm.

Sources

“Scissors,” Keyboard Layouts Doc (3rd edition)