Najjar, L. J., Stanton, B. C., Bowen, C. D., & Benel, R. A. (1988). Keyboard heights and slopes for standing typists (TR 85.0081). Rockville, Maryland: IBM Corporation.
LAWRENCE J. NAJJAR1, IBM Corporation, Rockville, Maryland, BRIAN C. STANTON2, and CHARLES D. BOWEN3, Essex Corporation, Alexandria, Virginia and RUSSELL A. BENEL, IBM Corporation, Rockville, Maryland
The purpose of this research was to assess the comfort, speed and accuracy of using keyboards while standing. Eighteen experienced typists participated in a typing task at three different keyboard heights and three different keyboard slopes. Typing speed and accuracy were measured and each participant completed an opinion questionnaire regarding comfort. As expected, there was a significant interaction between keyboard height and slope for typing speed without significant main effects for keyboard height or slope. When the keyboard was at a low height, performance at a flat and negatively sloped keyboard was significantly better than when the keyboard was at a more typical positive slope. The subjective results from the opinion questionnaire support these findings.
There has been an increasing use of computer terminals and keyboards while standing, including airline reservations representatives, bank tellers, and retail check-out clerks. Although seated keyboard height and slope have been investigated (e.g., Miller and Suther, 1983; Grandjean, Hunting, and Pidermann, 1983), there is no generally available empirical guidance for standing keyboard height or slope.
The importance of this issue is underscored by the potentially greater variety of keyboard placements at a standing work station. Although seated work surface heights tend to be standardized to typing or desk height, standing work stations must account for other factors. For example, operational requirements to view over or beside the top of the data entry and display devices have profound impact on the position of a keyboard for standing users.
The typical, positively sloped keyboard is reasonably comfortable for a seated person. The person's elbows are bent to allow the hands to extend over the keys and the wrists are angled up slightly to match the slope of the keyboard. Howver, if a keyboard is placed at a low height, such as on a desktop, a standing person is required to bend their wrists up at an uncomfortable angle. If view over the work station is required, as in air traffic control tower operations, it may not be possible to raise the keyboard to compensate for this uncomfortable wrist angle. A flat or negatively sloped (back row lower than front row) keyboard may relieve this discomfort and improve performance.
This study examined standing typing performance and preference at three keyboard home row heights and angles. The keyboard home row heights were 74 cm, 99 cm, and 125 cm. The keyboard heights were selected by applying minimum, middle, and maximum recommended seated typing elbow angles (Human Factors Society, 1988) to the anthropometric characteristics of a projected 1985 50th percentile standing person (NASA, 1978). The keyboard angles were flat, positively sloped 15 degrees, and negatively sloped 15 degrees.
Based on seated elbow and wrist angles, it was expected that the standing typist would perform better and prefer the positively sloped keyboard at the high and middle height because the arms are in a position similar to that for seated typists. The flat or negatively sloped keyboard was expected to facilitate performance and be preferred at the lower height because these keyboard angles provide more comfortable wrist angles than the positively sloped keyboard.
The eight female and ten male participants were technical employees of a large computer company. All participants were experienced typists. The participants were separated into six height groups that covered an equal portion of the range from the shod 5th percentile female to the shod 95th percentile male. To account for shoe heels, 2.54 cm was added to the MIL-STD-1472C (Department of Defense, 1984) height ranges. Each group consisted of three persons. The participants were tested individually.
Anthropometry equipment (GPM model 113) was used to measure the shod height, elbow height, and hand length of each participant. A goniometer measured standing elbow and wrist angles at each keyboard angle (see Figure 1). An IBM PC XT4 computer, monochromatic display, and keyboard were mounted on an adjustable video display terminal workstation. The height of the keyboard was changed by mounting the keyboard on stages placed on the workstation's keyboard work surface and adjusting the height of the workstation's keyboard work surface. The slope of the keyboard was changed by placing small stages under the front or rear of the keyboard. For the seated practice trial, the keyboard home row height was 79 cm and the keyboard slope was five degrees. Keyboard slope was measured from the horizontal off a plane through the key surface centers of keys in the bottom ("Z") and fourth ("1") rows. The middle of the display surface was at a height of 118 cm.
Figure 1. Angles and Heights.
For the three standing test trials, the keyboard was flat, positively sloped 15 degrees, and negatively sloped 15 degrees. The order was counterbalanced across keyboard heights. For each participant, the keyboard home row height was either 74 cm, 99 cm, or 125 cm for all standing trials. The keyboard home row height was counterbalanced between height groups. For the standing test trials, the middle of the display surface was at a height of 142 cm (see Figure 1).
Proprietary software allowed each keystroke to be captured, time-stamped, and checked for accuracy.
Each participant completed a consent form and typing background questionnaire, performed the typing tests, and completed an opinion questionnaire. Additonally, anthropometric measurements were taken.
There was one practice test and three experimental typing tests. The typing tests, from a college typewriting textbook (Wanous, Duncan, Warner, and Langford, 1980), were of equal difficulty. The order was counterbalanced across keyboard heights.
Each test consisted of 20 lines of text and required that each keyboard letter and number, plus some shifted characters, be pressed. One line of the text to be entered appeared at the bottom of each display. The characters typed by the participant appeared at the top of the display. The participant pressed the return key at the end of each typed line. This caused the next line of the text to appear at the bottom of the display.
Participants were asked to type as quickly and as accurately as possible. The typing tests were timed and errors were recorded. When a typing error was made, the computer emitted a tone and the display cursor stopped. Participants were required to press the back space key and correct the error before continuing. Each typing test took about 10 minutes to complete. There was a bread of approximately two minutes between tests while the experimenter changed the keyboard slope and reset the software.
After the typing tests, the participants completed the opinion questionnaire. The questionnaire included five point bipolar scales to reflect each keyboard angle on comfort, typing speed, and typing accuracy.
Two 3 x 3 mixed model analyses of variance were used to analyze typing speed and errors. For both speed and errors, there were no reliable main effects for keyboard height or slope. Considering speed, however, the main effect for keyboard slope approached significance (F(2,30)=2.64, p=0/09) and the interaction of keyboard height and slope was significant, (F(4,30)=3.64, p<0.05). The interaction is illustrated in Figure 2. There were no statistically significant interactions for errors based on keyboard height or slope.
Figure 2. Interaction of Keyboard Height and Slope.
Since the significant interaction indicated that typing speed differed for different keyboard heights depending on the slope, the simple main effects were calculated for each keyboard height across keyboard slopes. Three separate one-way analyses of variance were calculated using only the data for each of the three keyboard heights. Only in the low keyboard height condition was the effect of keyboard slope found to be significant, (F(2,10)=8.08, p<0.01). A Newman-Keuls post hoc test showed that both the flat and the negatively sloped keyboard produced significantly faster typing speeds than the positively sloped keyboard when the shelf height was low, (p<0.05)
A Kruskal-Wallis test was used to analyze the opinion questionnaire responses. The ratings for flat keyboard and positively sloped keyboard comfort differed significantly over keyboard heights (F= 4.89 (2,15) and F= 5.07 (2,15), respectively, p<0.05) as did the perception of how fast the participant typed using a positively sloped keyboard (F= 4.59 (2,15), p<0.05). Mann-Whitney tests were then calculated for each pairing of keyboard heights. It was found that both the flat and positively sloped keyboards were rated as being more comfortable when the keyboard height was high than when the keyboard was at a low height (U= 4.0, p<0.05) and more comfortable when the keyboard height was medium than when the keyboard was at a low height (U= 4.0, p<0.05). There was no significant difference between high and medium keyboard heights for flat or positively sloped keyboard comfort ratings. Those participants using a positively sloped keyboard at a high keyboard height perceived themselves as typing faster than when the positively sloped keyboard was at a medium or low height (U= 6.0, ps<0.05). There was no significant difference between medium and low keyboard height for perceived typing rate at positive keyboard slope.
The analysis of the anthropometric data indicated that there was a main effect for keyboard height on both arm angle (F=32.71 (2,17), p<0.001) and wrist angle (F=12.70, p<0.001). There was no main effect for keyboard angle, and no interaction of keyboard height and angle on either arm or wrist angle.
To maintain comfort, speed, and accuracy while standing, keyboards may require a different slope than that typically found on keyboards for seated users. Additionally, the keyboard slope for standing users may differ at varying keyboard heights. In the present experiment, neither height nor slope affected performance significantly when considered separately. However, the combination of height and slope did affect typing speed. When the keyboard was at a low height, performance on a flat and negatively sloped keyboard was significantly better than when the keyboard was at the more typical positive slope. A possible explanation for these results is that the posture of the standing typist at the low, positively sloped keyboard was uncomfortable. A person standing at a low, positively sloped keyboard is required to bend their wrists up at an apparently awkward angle. The observed decrease in performance may have been caused by the uncomfortable angle at which the participants had to bend their wrists.
The subjective findings support this interpretation. When the participants were asked to rate the keyboard slopes on comfort, the positively sloped keyboard was rated worst at the low height. The same was true for the flat keyboard. Since the participants were not asked to compare keyboards on comfort, it was not possible to determine whether both keyboards were equally uncomfortable. The flat keyboard may not have been uncomfortable enough to hamper performance because, at the low height, the flat keyboard was associated with significantly better performance than the positively sloped keyboard.
In addition, participants believed that they typed faster on the positively sloped keyboard at the high keyboard height than at the medium or low keyboard heights. This finding is consistent with the determination that the participants were more comfortable on the positively sloped keyboard at the high keyboard height than at the low keyboard height.
The finding that the effect of slope on typing speed approached significance may also be explained by typing posture. Once the keyboard height drops below the high level, the standing typing posture deviates from the posture used by seated typists. At lower heights the negative or flat slope of the keyboard may become an asset by allowing the standing typist to use a more comfortable wrist angle. The point at which the lines cross on Figure 2 may be where the negative and flat slopes start to facilitate standing typing. This point is at about 110 cm. Figure 3 indicates that at a keyboard height of about 110 cm, the positively sloped keyboard produces smaller wrist angles than either the flat or negatively sloped keyboards. Although the differences between the lines are not statistically different, the differences in wrist angles suggest that the larger wrist angles allowed by the flat and negatively sloped keyboards may facilitate typing at heights lower than approximately 110 cm.
Figure 3. Keyboard Height and Wrist Angle.
Each of the results of this experiment may be explained by the arm and wrist angles in the experimental conditions. Keyboards are used typically at a seated position and are sloped positively. At the high keyboard height, arm and wrist angles of standing typists most closely corresponded to those of seated typists. Therefore, it was reasonable to expect that, at the high keyboard height, the keyboard that is positively sloped would be associated with the best performance and preference scores. Since the only significant performance difference was for typing speed, the correlation between typing rates in each keyboard slope condition and the anthropometric measures was examined. Keyboard height and anthropometric measures of elbow angle, wrist angle, elbow height, and hand length were used to calculate stepwise multiple regressions. The typing rates for the three keyboard slopes were the dependent variable. The only consistent predictor of typing speed was wrist angle (ps<0.05). Wrist angle was correlated positively with typing speed. As the angle of the wrist (measured between the back of the hand and the forearm) increased, the typing speed increased.
The results of this study suggest that when a standing operator uses a keyboard at a low height, the keyboard should be flat or negatively sloped. Wrist angle appears to be the major factor that affects standing typing performance and comfort at different keyboard heights and slopes.
We are grateful to Regis Magyar for his generous assistance with they keystroke capture software. This study was performed under Federal Aviation Administration contract number DTFA01-84-C-00039.
Department of Defense. (1984). Human engineering design criteria for military systems, equipment and facilities (MIL-STD-1472C, Notice 2). Philadelphia: Naval Publications and Forms Center.
Grandjean, E., Hunting, W., and Pidermann, M. (1983). VDT workstation design: Preferred settings and their effects. Human Factors, 25, 161-175.
Human Factors Society. (1988). American National Standard for Human Factors Engineering of Visual Display Terminal Workstations (ANSI/HFS Standard No. 100-1988). Santa Monica, California: Human Factors Society.
Miller, W., and Suther, T. W. (1983). Display station anthropometrics: Preferred height and angle settings of CRT and keyboard. Human Factors, 25, 401-408.
NASA. (1978). Anthropometric source book, Volume I: Anthropometry for designers (NASA reference publication 1024). Yellow Springs, Ohio: Webb Associates.
Wanous, S. J., Duncan, C. H., Warner, S. E., and Langford, T. E. (1980). College Typewriting. Cincinnati: South-Western Publishing.
LAWRENCE J. NAJJAR, BRIAN C. STANTON, CHARLES D. BOWEN, and RUSSELL A. BENEL (Keyboard Heights and Slopes for Standing Typists)
LAWRENCE J. NAJJAR is a human factors engineer/scientist with IBM Corporation, in Rockville, Maryland, where he works on a Federal Aviation Administration project to modernize the air traffic control system. He has worked on keyboard layouts, performed ergonomic analyses of tower and control room work stations, and designed user-system interface software for ease-of-use. He earned a M.S. in engineering psychology from the Georgia Institute of Technology in 1983. His interests include the human-computer interface, the application of advanced technology to improve system usability, and ergonomics.
BRIAN C. STANTON is a human factors engineer with IBM's Systems Integration Division on the FAA's Advanced Automation System in Rockville, Maryland. He is currently a member of the team developing the training procedures and materials for the new air traffic control system. He has developed interfaces for the Voice Switching and Control System, a communication system for the en-route air traffic controllers. He has been involved in research on touch screen activation areas and CRT text legibility. He received an M.S. degree in psychology from Rensselaer Polytechnic Institute in 1985. He is interested in computer-human interface design and the use of advanced graphics for information presentation.
CHARLES D. BOWEN is a human factors engineer with Dynamics Research Corporation in Wilmington, Massachusetts. He received his M.S. in psychology from Rensselaer Polytechnic Institute in 1986 with concentrations in human factors and industrial organizational psychology. He is presently working with the Electronic Systems Division of the U.S. Air Force for the MILSTAR Terminal Program Office on human factors considerations in terminal development. Before joining DRC he was sub-contracted to IBM where he worked on the design team tasked to develop the man-machine interface for the Advanced Automation System for air traffic control.
RUSSELL A. BENEL is Manager of Human Engineering on the Advanced Automation System (AAS) program for IBM's Systems Integration Division in Rockville, Maryland. AAS is the next generation air traffic control system for the U.S. Prior to joining IBM in 1984, he was manager of the Human Factors Engineering Department at Essex Corporation. He received his B.A. from Washington and Jefferson College and an M.A. from Fairleigh Dickinson University prior to entering the U.S. Air Force. He served four years at the U.S. Air Force School of Aerospace Medicine performing research on human performance in unusual environments and under a variety of stressors. He received his Ph.D. in 1979 from the University of Illinois at Urbana-Champaign in engineering psychology. He returned to the School of Aerospace Medicine as a National Research Council Postdoctoral Associate. His professional interests include visual performance, complex system design, judgment and decision making.
1Request for reprints should be sent to Lawrence J. Najjar, IBM Corporation, 9201 Corporate Blvd., 861/4D37, Rockville, MD, 20850.
2Currently with IBM Corporation, Rockville, MD.
3Currently with Dynamics Research Corporation, Andover, MA.
4PC XT is a registered trademark of the International Business Machines Corporation.