Every product must be dealt with by a human, if only to turn it on. It is surprising in how many ways a product which is easy and clear to its designer can be difficult or confusing to the person who receives it. Many misfortunes, small and large, have resulted from bad design in this respect, and much pleasure and satisfaction have resulted from good design. The first major study of what is now called "human engineering," "human factors," or, to be fancy, "ergonomics," was made in the design of the airplane cockpit, where the pilot has little time in which to respond to many inputs with many outputs and there is a terrible price for error.
Many books and articles have been written on the subject, but they are rarely included in undergraduate programs. This article is a brief survey of the subject.
Simplest Rule
Imagine yourself in every possible relationship between a human and your product, and ask yourself how you could miss or misunderstand what is going on, how you could do the wrong thing at any time because of ignorance or confusion, and how you could make it easier to see, hear, and do what must be done.
Fourteen Specific Rules and Principles
- You should conform to conventions and not be "creatively" different unless you have very good reason. The Three Mile Island disaster in 1979 was due in part to the use of red lights to indicate normal conditions and green lights to indicate trouble! The poorly trained operators reacted to the usual (reverse) meaning of the colors and overrode perfectly well-operating automatic safety controls to generate the catastrophe.
- Your product should not injure operators or bystanders either catastrophically or gradually. Provide guards, safety switches, interlocks, warning lights, color patterns, and whatever else you can think of to prevent an ignorant, careless, or tired person from being hurt mechanically, electrically, or chemically. Prevent gradual injury from noise, bad lighting, or frequent tolerable stress. (There is something called "tunnel carpal syndrome" which comes from operating pushbuttons or switches too frequently under certain conditions.)
- A word about safeties and interlocks on production machines: operators try to disable or bypass them to make their jobs faster and more convenient. In effect there is a contest between design engineer and operator to save or lose fingers and hands.
- The product should be physically easy to operate. Forces and torques should be within easy effort of the weakest people who will operate it. Reach required should be within convenient distances for small people.
- We depend on touch as well as sight to identify controls and position, especially in the dark or when our eyes are fixed to something else. The electronic and aircraft industries have large families of knobs of different sizes, shapes, and textures to prevent errors.
- Color and color patterns (e.g., black and yellow stripes) are useful in identifying the meaning of signals, identifying control knobs, buttons, and levers, and warning of unsafe regions and objects. A large set of symbols has been standardized for international use to convey messages without words.
- Illumination has been going on for so long and in so many places that it is remarkable how badly it is sometimes done. There is an Illuminating Engineering Society which will be glad to send you literature. You should avoid lamps which shine directly into your eyes, glass or polished surfaces so oriented that they reflect light directly into your eyes, and very non-uniform brightness of displays.
- An operator should be comfortable enough so that there is no fatigue which would slow responses but not so comfortable that sleep is likely. Similarly, the operator should not be so busy that fatigue is likely but not so idle that important signals or observations are missed.
- The number of information displays is important: too much information is fatiguing and masks important information, while too little fails to give the operator what is needed. There is an opportunity, in complicated products, to use blinking, brightness change, color change, warning lights and sounds, and other means to attract the operator's attention to urgent information.
- Whenever an operator moves a control, there should be a response so that the operator knows he or she has succeeded in the control action. Joysticks on airplanes with power-driven control surfaces are provided with actuators to generate artificial resistance so that the pilot feels as if he or she is flying an airplane with directly coupled controls. Pushbuttons should move in response to pressure, or there should be a light or sound or other feedback so that the operator knows a contact has been made.
- Inputs and indicators for different portions of a system should be grouped together.
- The choice of digital or analog displays is largely a matter of fashion. Where resolution of three significant figures or more is required, only digital displays are easily read.
- Products should fail safe; that is, failure should result in a stopped rather than a runaway condition or should not otherwise result in human hazard. Furthermore, it is desirable that products should fail soft; that is, they should deteriorate in a noticeable way before they fail altogether so that the operator is given notice of imminent total failure before it happens.
- Not only should products resist harming humans but they should be resistant to harm by humans. One form of such resistance is "foolproofing," i.e., resistance to erroneous operation which is not malicious.
Human engineering yields better cooperation between product and people.
