Keyboard
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Keyboard layout
Long existing standards dictate the location of most of the keys, such as the
numbers, letters, symbol keys and the standard function keys, such as shift,
new line and backspace. These keys are in the "touch" area and account
for most of the keystrokes the user makes without breaking rhythm and losing
speed. Special function keys, such as CLEAR are in nontouch locations and can
be struck only if the user moves the hand away from the home position. They are
in the nontouch area because they are infrequently used and should be viewed
for verification before being struck.
The QWERTY layout is currently the most popular
keyboard configuration. It is named after the
first six keys of the upper left hand row.
It was developed in 1872 and laid out to slow
typists down somewhat and so prevent "jamming" of
mechanical typewriters. The DVORAK layout was
proposed in 1932 as a faster and more efficient
layout (Dvorak, 1943). This layout places the
most frequently used keys on the home row.
While it can be shown to be an improvement
over the QWERTY layout, the magnitude of the
advantages have not been shown sufficient to
justify retrofitting keyboards and retraining
typists. Thus, it currently has limited acceptance.
Key mechanism
Efficient keying requires that keys function
with minimum adequate force and with sufficient
displacement to provide muscular feedback to
the user. Key forces for current highproduction
keyboards are in the range of 0.40 to 1.25
newtons with key displacements of 3 to 5 mm.
Key spacing, key travel, force and key feedback
are keyboard characteristics generally agreed
on by most manufacturers and are specified
by ISO 9241 - Part 4 as follows:
"The horizontal and vertical distances
between two adjacent keys in the alphanumeric
and the numeric zones measured centre to
centre shall be 19mm +/- 1mm. Outside the
alphanumeric and numeric zones, other centre-line
spacings are permitted, but should not be
smaller than 15mm."
"The key displacement shall be between
1,5 and 6,0 mm."
"The preferred key displacement should
be between 2,0 and 4,0 mm."
"The force at the charcter generation
point or the snap point should be between
0,5 N and 0,8 N and shall be between 0,25
N and 1,5 N."
The more proficient the user, the lighter
the touch can be. If too little force is required,
however, extra keys may be struck accidentally,
and if too much force or displacement is required,
some keys may fail to be actuated because the
user did not press hard enough. Also, excessive
force induces finger fatigue. There is evidence
(Kinkead and Gonzales, 1969; Alden, Daniels
and Kanarick, 1972) that optimum force/displacement
characteristics of a key require a steadily
increasing force as the key is depressed until
contact is made. Immediately beyond that point,
the force is sharply changed so that users
can easily "feel" when the key has
been pressed sufficiently. A typical force
displacement curve for a key with tactile feedback
is shown in.
A force displacement curve for a
key with tactile feedback (Clare, 1970).
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