AFB TECH has defined three classes of controls that cover the range of accessibility that we observe on the market. These three classes include "accessible controls," "inaccessible controls," and "ambiguous controls." We defined these classes as follows.
Accessible Controls
Accessible controls are those that have historically been provided on appliances, including conventional turn knobs, such as those that are found on stove burners and dryers. Mechanical push buttons that latch or change position when engaged also fall into this category.
In almost all instances, accessible controls can be felt to determine their status. On a stove, reaching to feel the burner control at the 9 o'clock position would let the cook know that the burner is set to simmer. Feeling the pointer of the dryer control periodically as the cycle progresses would allow the user to predict how much longer the cycle will take. Of the three classes of controls, these are the only ones that allow a person who is blind both to position the appliance settings and to confirm those settings independently while the appliance is operating.
Inaccessible Controls
These provide no means of direct tactile identification or direct observation of the status of the appliance. They are typified by the flat touch panel that is found on the majority of microwave ovens and many other appliances, such as wall ovens and dishwashers.
Inaccessible controls require modification to be usable nonvisually. In some instances, even modification, such as the use of braille or other tactile markings, cannot mediate the inaccessible behavior of the control.
Ambiguous Controls
Ambiguous controls fall in between the accessible and inaccessible classes. The ambiguous control provides at least some feedback to the user. Examples include oven controls that set a default temperature of 350 degrees when turned on. Pressing textured regions on the smooth control panel activates the controls. Pressing the Up and Down controls increases or decreases the temperature by 5 degrees for each press of the control.
In addition to changing the temperature, a distinct beep is heard as each control is pressed. By counting beeps, one can set the temperature accurately. Direct verification of the temperature is not provided because direct observation of the display is not possible with the electronic oven control. This ambiguity creates a situation in which it is possible to set the oven nonvisually, but full independent access to the information on the display is not provided.
