The
basic objectives in keyboard form factor are to minimise the
size of the unit, provide for logical key layout and create
a proper slope.
Minimising size is important because it means more room for
other items on the work surface. Also, minimising keyboard thickness
and height permits maximizing knee space below.
Slopes of 10 to 15 degrees are typical, but other slopes may
be considered for specific applications and locations. Recent
focus has been placed on complying with the International Standard
ISO 9241-4:1998(E) “Ergonomic requirements for office work with
visual display terminals (VDT)- Part 4, published by the International
Organisation for Standardisation (ISO) in 1998.
ISO requires that the home row should be not more than 35mm
above the table surface with 30mm being the preferred height.
ISO also recommends that the keyboard slope should be 5-12 degrees
positive to the horizontal. The slope of the unadjusted keyboard
shall be between 0 and 15 degrees positive.
Both the height of the home row and the slope of the keyboard
are thought to reduce user strain and fatigue, although there
is still debate over the actual benefits of this design.
Other user considerations may be incorporated into the keyboard
package so long as they do not interfere with basic operations
or make positioning the keyboard more difficult. For example,
if a palm or wrist rest is added, it should be designed so that
it does not interfere with normal keying.
Cursor
control keys
The
cursor on the VDT screen is a position-marking symbol, such
as a solid block or underscore. It may blink or be brighter
than other symbols to identify its location easily. In test
display applications, the cursor control keys may be used
to relocate the cursor to a desired position. Four keys are
marked with arrows for the four rectilinear directions of
possible movement. These keys are usually "typamatic," that
is, if the key is depressed for more than about half a second,
a sequence of movements at a variable or fixed rate, such
as 10 steps per second, will occur. Single steps are generated
when the keys are kept depressed for less than half a second.
In the discussion of cursor control, ANSI makes the following
statement:
"Two dimensional cursor control (e.g., cursor keys, a "mouse,"
trackball, etc.) shall be provided for text processing applications.
If cursor keys are provided they shall be arranged in a two
dimensional layout, for example, in a "box," a "cross," or
inverted T format. If the cursor keys are not dedicated, that
is, have collateral functions, their functional status shall
be clearly indicated."
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