Chapter 10 - Input and Output Devices

Question 1

Visual Displays

Answer 1

Requirements are developed by combining characteristics of

Human Information Processing with information gathered during task analysis

Question 2

Favor visual presentation if:

Answer 2

The auditory sense of the user is overburdened.
The message is complex and/or long.
The message deals with a specific location on a panel.
The message must be referred to later.
The user works primarily in one location.
The receiving location is so noisy that some auditory messages may be missed or misheard.

Question 3

Other Major Considerations:

Answer 3

1. Type of display
2. Information content and format
3. Physical characteristics

Question 4

Electronic Displays

Answer 4

Advantages: High writing speed, high resolution, full color capabilities, full range of gray scales, storage capability, large range of screen sizes.

Disadvantages: Bulkiness of the equipment, curvature of the screen, high voltage required, relatively delicate equipment (vacuum tubes), limitations of maximum screen size.

Question 5

Color Coding

Answer 5

Colored lights are generally used in situations that change and where the environment is not fixed.

Lights can also flash on and off as an attention-getting device.

Brightness and rate of flash are only moderately useful when coding information- better to vary only 2 properties : Color and on/off status.

Don’t use color to indicate conditions contrary to what they typically represent.

Question 6

Avoid color mismatches such as

“Green” in purple letters

Answer 6

Tends to slow down identification of its color.

Slows down reading.

May impede the performance of concurrent activities.
Can contribute to misidentification of word or message.

Question 7

Limit Coded Information

Answer 7

Three Mile Island – over 100 alarms, most of them visual, went off with no way of discerning the unimportant ones from the important ones.

Question 8

Factors Involved in Selecting a Coding Technique

Answer 8

1. The kind of information. A lot of information – Alphanumeric,
   on/off – a light
2. The amount of information to be displayed. Color not practical for many items.
3. The space requirements for the code.
4. Ease and accuracy of understanding.
   Interaction of displays at any given time.

Question 9

Code Discriminability

Answer 9

Permits the observer to distinguish one coded value from another. This requires recognition of the word, character, or symbol used for coding.

Question 10

Physical Characteristics of Displays

Answer 10

Important scale characteristics
Scale range – The numerical difference between the highest and lowest value on a scale.
Numbered- Interval value- The numerical difference between adjacent numbers on a scale.
Graduation- Interval value- The numerical difference represented by adjacent graduation marks.

Question 11

Scale Selection

Answer 11

Designer should decide on the
appropriate scale range and should
estimate the reading precision required.

Question 12

No Scale Interpolation

Answer 12

Quantitative scales should be designed for reading to the nearest graduation mark.

a. Graduation mark for each unit
b. Less space available – may be too crowded for accurate and rapid reading
c. A scale that requires interpolation- could increase reading errors

Question 13

Scale Layout

Answer 13

Numbers should *** in a clockwise direction on circular and curved scales,

from bottom to top on vertical straight scales, 

and from left to right on horizontal straight scales.

Question 14

Zone Marking

Answer 14

Indicate various operating conditions on many indicators such as operating range (upper, lower) or danger limits, caution, etc. The zone marking might be colored coded.

Question 15

Auditory Displays – Preferred When:

Answer 15

The message is relatively short

Response time to the message is important

The vision of the user is already overburdened

The receiving locations is not suitable for the reception of visual information

The user’s job requires considerable movement

Question 16

Common use of Auditory Displays- Alarms and Warnings

Answer 16

Considerable distance-> Loud, but low frequency, readily distinguishable.

Should cease only after the user responds appropriately to the cause of the alarm.

The sound made by any piece of equipment is to some extent an auditory display.  
For example, the sounds made by a disk drive when reading or writing a disk.

Question 17

Controls

Answer 17

Enable a user to make a change in the system and often are used with displays. Ex.: Keyboards, mice, steering wheels, knobs, levers, push buttons, etc.

Question 18

Controls Serve Four Kinds of Functions:

Answer 18

Activation- An on and off switch, or some other binary action.
Ex. Pressing keys on keyboard.

2. Discrete Setting – A control set to a position representing any of three or more discrete system responses.
   Ex. Automobile gear positions

Quantitative Settings- Individual settings of a control device that vary along some continuous quantitative dimension.
Ex. Volume adjustment on a radio

Continuous Control- Constant control of equipment
Ex. Steering an automobile.

Question 19

Consider Four Areas When Selecting A Control:

Answer 19

1. Function of the control- Purpose, importance, critical, minor adjustment, what does it affect
2. Task requirements- Degree of precision, how fast must the setting be made, emergency control
3. User information requirements- Can the user find it, how quickly must user work with it.
4. Work Layout- Where should it be located, availability of space, importance

Question 20

Consider Foot Controls when:

Answer 20

When the application of moderate-to-
large forces is necessary.

When the hands are overburdened.

Question 21

Coding Controls

Answer 21

The five most common methods for coding controls are labeling, color, shape, size, and location.

Question 22

The Choice of Coding Method Depends on the Following Factors:

Answer 22

1. Total demands on the user
2. Extent and methods of coding already in use
3. Illumination of the user’s workplace
4. Speed and accuracy with which controls must be identified
5. Space available for the location of controls
   Number of controls to be coded

Question 23

Labeling

Answer 23

The simplest way to indicate a control is to label it.

Question 24

General Recommendations for Labeling

Answer 24

Locate labels systematically in relation to controls
Design labels to tell what is being controlled
Make labels brief
Only employ unusual technical terms when absolutely necessary
Do not use abstract symbols
Use a letter and number style that is easily readable
Locate labels so they can be easily seen

Question 25

Color Coding

Answer 25

Most effective when a specific meaning can be attached to the color

Question 26

General Principles for Controls

Answer 26

1. Critical and frequently used controls should be located within easy reach.
2. The force, speed, accuracy, and range of body movement required to operate a control should never exceed the capability limits of the least capable user.
3. The total number of controls should be kept to a minimum.
4. Control movements should be as simple, easy, and as natural as possible.
5. Control actions should result in a positive indication to the user.
6. Control surfaces should be designed to prevent slipping.
7. Controls should be designed and located to prevent the probability of accidental operation.

Question 27

Grouping

Answer 27

When using a large number of controls and displays grouping should aid in determining:

Which control affects which display

Which control affects which equipment component

Which equipment component is described by each display

Question 28

Four General Direction-of- Movement Rules

Answer 28

1. The preferred direction of movement for most hand controls is horizontal, rather than vertical.
2. All the equipment that the same person uses should have the same controls-display motion relationship.
3. Control-Movement relationships are particularly important in vehicle movement.
   A movement of control to the right should result in a movement to the right, right turn.
4. The direction of movement of a control should be considered in relation to:
   * The location of the user relative to the control,
   * The position of the display relative to the control, and
   * The change resulting from the control movement.