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The Supreme Value of Adjustability
- By Thomas J. Albin
- Feb 28, 2008
Adjusting computer workstations improves office workers' comfort and health.
The ability to adapt the workplace to the size variation among computer workers is critical to both promoting users' comfort and protecting their health. While adjustable workstations are commonly thought of in terms of adjusting heights and depths to accommodate differences in sizes of users, it is also important to recognize the importance of adjusting computer workstations to accommodate differences in tasks.
A computer worker who interacts with customers face to face requires a different workstation than one who interacts with customers via telephone. Moreover, the types of tasks performed often vary throughout the workday and the workstation must accommodate, or adjust to accommodate, these changes in tasks in order to maintain user comfort and productivity. Consequently, it is important to consider how to accommodate the variation in tasks the computer user performs, as well as the variation in their own individual characteristics, when designing a computer workstation.
Most Common Types of Discomfort
Visual discomfort, such as dry eyes and headaches, and neck and shoulder musculoskeletal discomfort, such as sore stiff neck and shoulder muscles, are the most common types of discomfort reported by office computer workers. All of these can be alleviated by a mindful arrangement and adjustment of computer workstations.
Three types of adjustments to workstations are effective in alleviating these problems: monitor support and placement, keyboard and mouse placement, and forearm support.
Monitor Support and Positioning
Variation in users and user tasks dictate the need for monitors that adjust vertically and horizontally. Variation in eye height between the tallest and smallest individuals in the U.S. population is in the neighborhood of 9 to 10 inches. This variability is a prime reason for the need for monitor height adjustability. Although the weight of CRT monitors often made this difficult to achieve in the past, the increasing use of lighter-weight flat-panel displays and adjustable mounting solutions now make this readily achievable.
Vertical monitor placement
Vertical monitor placement plays a key role in both visual comfort and in neck and shoulder comfort. A monitor that is placed too high typically causes the user to tilt his or her head and neck back while looking at the monitor; this static extension fatigues the neck and shoulder muscles and quickly becomes uncomfortable. At the same time, looking up at a monitor causes difficulties for the eyes as well as the neck and shoulder muscles. A larger portion of the surface of the eye is exposed, which accelerates drying of the protective, lubricating tear layer. Although the tear layer is renewed as the computer user blinks, the drying effect is compounded by the decreased rate of blinking observed during visually demanding tasks.
It is also more difficult for the eye to focus on near objects (such as computer screens) when they are elevated relative to the level of the eyes and easier to focus on near objects that are below eye level. However, anyone who has attempted to focus on the tip of his or her nose knows firsthand the discomfort associated with focusing on a too-near object, even when it is below eye level! A too-low placement of the monitor also causes the user to tilt his or her neck and head forward; now, it is static flexion of the neck and shoulder muscles that leads to musculoskeletal discomfort.
So what is the optimal solution for vertical monitor placement? Current research1 and technical standards2 recommend that the vertical placement of the monitor be such that the center of the screen is approximately 15 to 25 degrees below horizontal eye level.
This is in good agreement with the commonly used advice to place the top of the viewing area of the screen at or slightly below eye level. For example, the center of a 21-inch diagonal screen viewed at the minimum recommended viewing distance2 of 20 inches would be about 15 to 17.5 degrees below horizontal eye level for screens with 4:3 and 16:9 aspect ratios, respectively, if placed in this manner.
Alternatively, the angle can be estimated based on the horizontal distance between the screen and the users' eyes and the position of the center of the screen below horizontal eye level. At 15 degrees, the center of the screen is about one-fourth of the viewing distance below eye level; at 25 degrees, the center of the screen is slightly less than one-half the viewing distance below horizontal eye level.
Viewing distance
The distance between the monitor and the users' eyes also affects visual comfort and neck and shoulder comfort. Placing the monitor too close to the users' eyes causes discomfort as the eyes turn inward (converge) in order to focus on a near object (the screen) and the ciliary muscles attempt to reshape the lens in order to bring the screen into focus.
This article originally appeared in the March 2008 issue of Occupational Health & Safety.