How many times have you used the handicap button next to a door in order to open it? While you could have just pushed or pulled on the door to make it open, you decided to use the button next to the door. Many times I find myself pressing the button because it is easier than opening the door. Rarely do I take the time to think of why that button is there. If I can just open the door manually, why would a button be available as well? The answer seems fairly obvious; some people are not able to open the door manually. During the design process, one must take human variability into account. Human variability is defined by Wikipedia as “the range of possible values for any measurable characteristic, physical or mental, of human beings.”
This plays a huge role in the design of the door because many different types of people are unable to use the door or only could with difficulty. If a war veteran who lost his arms wants to enter a building but could not easily open the door, it is reasonable to have an easier way to open the door. The push button has other positive externalities. If you have your arms full or are wheeling around a stroller, it is simply more effective to use the push button.
Luckily an electronic push button is not a complex structure to construct. The circuit works because when the button is not pressed the circuit is open, so there is no current flowing through the circuit. Thus, the button works because “when we push the button the circuit closes and current flows: the LED will be on.” (Varesano) This simple circuit is used millions of times every day by Americans, and it makes entering and exiting buildings much easier.
One type of design for human variability is a laptop for the blind.
http://www.youtube.com/watch?v=ldM11pHa2OU
This design is centered about the sense of hearing. The speakers for this specific model are located under the keyboard. They must be the most effective speakers on the market in order to maximize the capabilities of the computer. The computer talks to you and tells you what keys to press for various functions. The keyboard itself is in braille, and various shortcuts will lead to the functions of the computer (such as pressing the “e ” key in order to hear e-mails). Because a monitor is unnecessary, the laptop is not going to be astronomically expensive.
http://www.youtube.com/watch?v=ldM11pHa2OU
http://en.wikipedia.org/wiki/Human_variability