Tenix Defence Universal Principles of Design Prepared by: Anthony Royle Systems Engineer Approved...
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Tenix Defence Universal Principles of Design Prepared by: Anthony Royle Systems Engineer Approved by: Malcolm G. Tutty P-3 CENGR August 2006
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Transcript of Tenix Defence Universal Principles of Design Prepared by: Anthony Royle Systems Engineer Approved...
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Universal Principles of Design
Prepared by:
Anthony Royle
Systems Engineer
Approved by:
Malcolm G. Tutty
P-3 CENGR
August 2006
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Presentation Brief Design is a diverse discipline
We apply a very specific subset
This presentation will introduce conceptswhich should be considered when designing
For details of specific topics, refer to:Universal Principles of DesignWilliam Lidwell, Kritina Holden, Jill ButlerISBN1-59253-007-9
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80/20 Rule
A high percentage of effects in a large system are caused by a low percentage of variables
80% of a products use involves 20% of its features 80% of progress is from 20% of the effort 80% of errors come from 20% of components 80% of a company’s income comes from 20% of its products 80% of innovation comes from 20% of people
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80/20 Rule
In design, we should: Identify the 20% of functions used the most and make them
easily accessed Not all elements are equal - avoid complex areas with little real
benefit Avoid estimating based on the fastest 80% of a task
GUIDE LINES
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Accessibility
Objects and environments should be designed to be usable by as many people as possible
Historically this focussed on disabilities Advantages are applicable to wider audience Primary attributes:
• Perceptibility – use of multiple senses (sight, sound, feel)
• Operability – minimal physical exertion
• Simplicity - intuitive, clear interface
• Forgiveness – reduce severity of mistakes
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Accessibility Use multiple coding methods for information:
• Colour and icons
• Text
• Tactile controls
• Audible feedback
• Minimise repetitive actions Avoid need for sustained physical effort Consistent and clear interface Use progressive disclosure to only present relevant controls Clear feedback for actions Design to minimise consequence of mistakes, using:
• Confirmations
• Warnings
• interlocks
GUIDE LINES
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Aesthetic-Useability effect
Aesthetic designs are perceived as easier to use
A phenomenon whereby an aesthetic design will be perceived as easier to use than a non-aesthetic design
Nokia experienced huge demand for itsphones with clip on covers
Customers may reject a functional design due to poor aesthetics
Long term user satisfaction also driven by aesthetics
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Affordance
A property in which the physical characteristics of an object influence its function
Some objects have fundamental uses, e.g. wheels roll, handles are for pulling, stairs for climbing
Humans have expectations of how standard objects behave
Designs which use objects naturally tend to be more successful, e.g. don’t use a handle on a door which should be pushed open
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Affordance Consider ‘expected’ behaviour of objects
Exploit intended function of objects
Good design will inhibit incorrect use;
• chairs which only stack one way
• lego blocks have a natural interlock
Computer Interface elements such as3D buttons are clearly ‘push’ operations, sliders obviously ‘slide’ between controlled limits. These are all natural to humans.
GUIDE LINES
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Chunking
Combining many units of information into smaller chunks to assist human memory and processing
Human short term memory holds 4±1 items
Lists bigger than this should be presented as ‘Chunks’
Familiar data items (words) may exceed this slightly, complex items (numeric values)need smaller groups
Does not apply to lists where the operator is scanning for a particular item; no attempt is made to remember multiple items
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Closure
A tendency to perceive a set of elements as a single pattern rather than individual elements
Humans will recognise a constructed shape before its components These pictures will be initially recognised
as circles, then as groups of lines
It may not be necessary to show all information;a simpler visual design may permit less clutter
Additionally, movement between snapshot frameswill be supplied by the viewer as seen in strip cartoons
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Colour
Colour is used to attract attention, group elements, indicate meaning and enhance aesthetics
The human eye can process about five colours at one time – don’t overuse colour!
Saturated colours (pure hues) attract attention Desaturated colours convey information efficiently Use warm colours for foreground elements and cooler colours for
background Don’t rely on colour to convey information; a significant proportion of
the population have limited colour vision
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Common fate (1)
Elements that move in the same manner are perceived to have a relationship
Similarity through movement is stronger than visual similarity
Affected by:
• Direction
• Speed
• Time at which objects move
• Proximity
Stationary objects are likely to be associated by appearance or position
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Common fate (2)Example of common fate
OXOOXOXXXOO
Stationary: Grouped by appearance
Moving: Grouped by fate
(click)
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Confirmation
Preventing unintended actions by requiring verification of actions before they are performed
Primarily used to prevent errors known as ‘slips’ Used to reduce likelihood of serious or dangerous actions occuring Two types of confirmation:
• Dialog – a confirmation request is displayed after the action is selected
– Suitable for non time critical actions, e.g. deleting a file
– Slows operator down
• Two-step operation – an enabling action must be performed before the critical action is selected, e.g. release safety catch
– Suited to time critical actions, e.g. firing a weapon
– Is usually more intuitive to an experienced user
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Confirmation Avoid over-use of confirmations Consider consequence of each action Two step may remain ‘armed’ after the event, e.g. a switch cover stays
‘flipped’ Dialogs should have a clear choice of actions, OK/Cancel is rarely
suitable
‘Undo’ functionality should be considered in place of a dialog
GUIDE LINES
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Consistency
The usability of a system is improved when similar parts are expressed in similar ways
Four kinds of consistency:
• Aesthetic Consistency
– Style, appearance, colour, logo
– Sets an expectation based on brand
• Functional Consistency
– Behaviour and sequence
– E.g. traffic lights all follow the same sequence
• Internal Consistency
– Items within a system work together
– E.g. Matching text fonts on a control panel
• External Consistency
– Agreement between dissimilar systems
– E.g. Open file formats
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Constraint
A method of limiting the actions that can be performed on a system
Constraints are used extensively in Aerospace systems
Can reduce errors or danger
Improved usability through clear limits on actions
Two types, each with subcategories:
Physical Psychological
Paths Symbols
Axes Conventions
Barriers Mappings
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Constraint – Physical (1)
Paths
Convert physical force to linear/curvilinear movement Using channels or grooves Also applicable to GUIs
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Constraint – Physical (2)
Axes
Convert physical force into turning motion Potentially infinite movement E.g. trackballs, radio tuning knobs
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Constraint – Physical (3)
Barriers Absorb or deflect movement around barrier Deny errant actions E.g. Rail crossing barriers, keyed plugs, walls
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Constraint – Psychological (1)
Symbols
• Communicate through text and symbols
• Warning signs, traffic arrows
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Constraint – Psychological (2)
Conventions Learned traditions E.g. Red light means ‘stop’ May be misinterpreted
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Constraint – Psychological (3)
Mappings Proximity of objects suggests a connection E.g. A switch beside a power point
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Control
The level of control provided by a system should be related to the proficiency of the people using the system
Understand the target user(s) of your system
Complex controls will confuse the inexperienced, simple controls will frustrate ‘power’ users
Systems can adapt their complexity E.g. windows apps hide complex
operations initially
Too much control can also introduce risk of accidental misuse
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Cost-benefit
An activity will only be pursued if its benefits are equal to or greater than the costs
Everything we do has a cost
• Time to read a book
• Price of a car We only decide to do something if the perceived benefit exceeds its
cost. In system design we must always consider the cost AND benefit of
features
• Some features are complex and appeal to engineers, but offer little benefit to the user. These should be avoided
• Some complex features may seem hard to implement, but offer great benefit to the user. We should still consider these.
Focus groups and usability tests help to determine benefit
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Development Cycle
Successful products typically follow four stages of creation Requirements
• Controlled interactions with users
• Knowledge of analysts Design
• Goal is a set of specifications that meet all requirements
• Use similar systems where possible Development
• Ensure specifications are maintained
• Reduce variability in parts and processes Testing
• Focussed on requirements and user needs
• Quality of modules and their integration
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Development Cycle - linear
The linear lifecycle Also known as waterfall Each phase is completed before the next is started Well suited to projects with fixed requirements
Requirements
Design
Development
Testing
(click)
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Development Cycle - iterative
The iterative lifecycle Also known as rapid prototyping Resulting system can be closer to user needs
Requirements
Design
Development
Testing
(click)
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Entry Point
A point of physical or attentional entry into a design Mostly associated with buildings, but also applications Systems which are obstructive to use are less likely to gain approval
or user support Three point strategy to assess a design
• Minimal barriers
– Avoid obstructing entry to program, e.g. slow splash screens, long start up times
• Points of Prospect
– Once inside, it should be clear how to reach the information required
• Progressive lures
– Make users want to explore deeper into the program
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Errors
An action or omission of action yielding an unintended result
Most errors classed as ‘human error’ but actually stem from poor systems
• Slips
– Action taken was not as intended
– Reduced by confirmations, affordances and constraints
• Mistakes
– Action taken was as intended but incorrect
– Can be reduced by
• Improved situation awareness, keep key indicators and controls within one eyespan of each other
• Reduced workload from better design
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Factor of safety
The use of more elements than is thought to be necessary to offset the effects of unknown variables and prevent system failure
Most systems are deliberately over-engineered for safety or performance
Factor of Safety is the number of times the spec is exceeded by FoS depends on level of ignorance of design parameters;
• Familiarity of techniques and processes
• Variability of chosen materials (steel more consistent than wood)
• Peak usage Examples
• Steel & Concrete structures – 2x to 4x
• Wood structures – 4x to 8x
• Internet services – 3x
• Great Pyramid at Giza – 20x
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Factor of safety
Safety also applies to meeting demand in processing systems
FoS increased by using extra material, processing power, better materials
FoS tends to be revised downwards on subsequent systems as process is better known; often until failure actually occurs.
• Titanic
• Space Shuttle
Rated Capacity x Fos = Design Capacity
Always use rated capacity when considering changes to system
GUIDE LINES
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Feedback loops
A relationship between variables in a system where the consequences of an event feed back into the system as input, modifying future decisions
Exist in most real-world systems Positive Feedback
• Amplifies system output, accelerating growth or decline
• Does not seek a particular output level
• Examples are finance markets which accelerate towards crashes Negative Output
• Dampens output to achieve a particular state or level
• Examples: Flight control computers, temperature thermostats, cruise controls
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Fitt’s Law
The time to move to a target is a function of the distance to target and the size of the target
E.g. Time to move a mouse pointer to an icon, or hand to a button
Two Distinct Components
• Ballistic Movement
– The large movement to get close to the control
– Depends on distance to target
– Reduced by physical barriers, e.g. edge of screen or lever end stops
• Honing Movement
– The small movement to centre on the target
– Depends on size of target
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Fitt’s Law
Useability of systems can be improved.
Place commonly used buttons near screen edges, e.g.
Context menus require little ballistic movement
Use larger controls for frequently used items
Example – car manual shift gearboxes are fast because:
• End stops limit ballistic movement
• The target (gear) is at a physical limit, needing no honing
GUIDE LINES
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Flexibility – Usability Trade-off
As the flexibility of a system increases, it’s useability decreases
Flexibility = Complexity
For example, a swiss army knife is flexible, but none of it’s functions are as good as a dedicated tool
Flexibility should be sought where user needs are not clear
Iterative development can be used to reduce flexibility
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Forgiveness
Designs should help people avoid errors and minimise the negative consequences when they do occur
Human error is inevitable
Forgiving Designs encourage user confidence
Mechanisms for forgiveness
• Affordances – guide users away from slips through design
• Reversibility – ‘Undo’, ‘Abort’ and ‘Self Destruct’
• Safety nets – protection from effects of errors e.g. ejector seats
• Confirmation – verification before actions
• Warnings – e.g. signs, prompts, alarms of imminent danger
• Help – online help or trouble shooting manuals
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Garbage In – Garbage Out
The quality of system output is dependent on the quality of input
Even well trained users can enter flawed information
Effects of bad data may not surface immediately, but can be severe
Effort spent during design of system input can have big benefits
• Protect system and users
• Less user frustration
Employ affordances and constraints such as listboxes, fixed choices
Enhance information quality with previews and confirmations
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Hick’s Law
The time it takes to make a decision increases as the number of alternatives increase
Applicable to simple decisions only, also excludes complex menus
A driver’s reaction time to a hazard will increaseif he has the option to swerve around it
Offer the fewest choices where response time is important
Response Time, RT = a + b.log2(n)
• a is pre-decision reaction time
• b is time per decision, typically 0.155 seconds for humans
• n is number of options
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Hierarchy
Hierarchical Organisation is the simplest structure for visualising and understanding complexity
Three approaches
• Tree
– Uses element size/position to show relationships
• Nests
– Drawn in a Venn Diagram style
– Elements are inside others
• Stairs
– E.g. Windows explorer
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Hierarchy of needs
In order for a design to be successful, it must meet people’s basic needs before it can attempt to satisfy higher level needs
Creativity
Proficiency
Usability
Reliability
Functionality
Highest Value - Allows users to create and explore areas beyond the original design
High Value - Empowers users to do more than they could before
Moderate Value - Easy to use, tolerates mistakes
Low Value - Operation is consistent and reliable
Little Value - Meets design requirements, e.g. play, record
Level of need
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Highlighting
A technique for bringing attention to an area of text or image
Some data we present will need highlighting to users Keep highlighting to a maximum of 10% of items; effect reduces Bolding is more effective than italics or underlining; less noise Uppercase TEXT is effective amongst lower case Font changes don’t stand out well Colour is effective when used sparingly with bold colours Inversing elements works with text, but often obliterates icons Reserve blinking for highly critical data. Offer an option to stop the
blinking
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Iconic representation
The use of pictorial images to improve the recognition and recall of signs and controls
Icons can save space and highlight information, e.g. error symbols Four types:
• Similar Icons
– Images look like the item they represent, e.g. bend in road
• Example Icons
– Images represent things associated with the item, e.g. an airplane for an airport
• Symbolic Icons
– An abstraction of the item represented; a lightning flash for electricity
• Arbitrary Icons
– Memorable but no resemblance to object, e.g. radioactive
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Interference Effects
A phenomenon in which mental processing is made slower and less accurate by competing mental processes
Conflict between human mental systems will slow user responses
• Stroop interference
– An irrelevant aspect of data items contradicts the primary meaning, e.g. RED BLUE
• Garner interference
– An irrelevant stimulus distracts attention from an item
– E.g. moving symbols next to text being read
• Proactive interference
– Existing memories interfere with new information
– E.g. when learning a second language, the original will interfere
• Retroactive interference
– Existing memories are affected by new learning
– E.g. Remembering a new phone may confuse and older one
(click)
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Iteration
A process of repeating a set of operations until a specific result is achieved
Design Iteration
• Desirable process
• An initial design is continuous refined, adding more detail until complete
• Feedback can be internal or from user groups Development Iteration
• Unexpected redesign necessary when building a product
• Result of poor design
• Costly and undesirable
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Layering
The process of organising information into related groupings in order to manage complexity and reinforce relationships in the information
Presentation of information is a common system function
Aim is to reduce complexity or size of information
• Two dimensional
– Primarily textual data
• Three dimensional
– Suited to geospatial data
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Layering – 2D
Two dimensional layering
Linear
Nonlinear
Beginning Middle 1 Middle 2 End
Transport
Air Ground
Plane Car Train
Hierarchical / Collapsible tree
Word Synonym
Word Synonym
Parallel; a table of values
Home
Info
Web; complex linked data
InfoInfo
Info
Info
Info
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Layering – 3D
Three dimensional layering
Present a basic image, with data overlaid Projection may be 2D or 3D
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Mental Models
People understand and interact with systems and environments based on mental representations developed from experience
Two types of Mental Models
• System Model
– Describes how a system works
– Typically well understood by designers, not users
• Interaction Model
– Describes how users interact with the system
– Well understood by users, but not designers
– Designers must strive to understand this
– Operational Concept Document
– Focus Groups, observation of users
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Modularity
A method of managing system complexity that involves dividing large systems into multiple, smaller self-contained systems
Complex or large systems should be considered as ‘modules’
Interfaces between modules should be well defined, and ideally simple
Allows third party suppliers to have competing designsm
Many systems become more modular as they evolve
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Ockham's Razor
Given a choice between equally functional designs, the simplest design should be selected
“Everything should be made as simple as possible, but not simpler” – Albert Einstein
Unnecessary design elements usually:
• Increase weight
• Increase Cost
• Decrease reliability
• Complicate maintenance
• Confuse users
The potato peeler
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Performance Load
The greater the effort to accomplish a task, the less likely the task will be successful
Increased load will increase errors and time to complete Load splits into two categories Cognitive Load
– Level of mental activity required
– Perception, memory, problem solving skills
– Improve by reducing visual noise, chunking and automation
• Kinematic Load
– Level of physical activity required
– Number of steps, physical force
– Improve by shortening distances, reducing steps by automation
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Performance vs preference
The designs that help people perform optimally are often not the same as the designs that people find most desirable
Users will often favour designs they like over designs that work better
Dangerous to rely solely on user feedback at workshops
Carefully observe user performance as well as their views
BUT users may not accept an optimal design if it is too different
• E.g. Dvorak keyboard is 30% faster than qwerty, but who wants one?
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Prototyping
The use of simplified and incomplete models of a design to explore ideas, elaborate requirements, refine specifications and test functionality
Three basic kinds
• Concept prototyping
– Concept sketches, storyboards
– Facilitate user workshops
• Throwaway prototyping
– Representative models
– Discarded after use
– Quick to produce
• Evolutionary prototyping
– Prototype will be refined in multiple steps
– Can become final product, e.g. computer GUI
– Risk of refining when radical redesign needed
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Redundancy
Use of more elements than necessary to maintain the performance of a system in the event of failure of one or more of the elements
Diverse Redundancy
• Multiple elements of diverse types
• E.g. Trains may have electric, hydraulic and pneumatic brakes Homogenous Redundancy
• Multiple elements of a similar type
• E.g. strands in a rope Active Redundancy
• Elements are all in use continuously
• E.g. Pillars supporting a roof Passive Redundancy
• Elements are swapped in when failure happens
• E.g. Spare tyre on a car
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Scaling Fallacy
A tendency to assume that a system that works at one scale will also work at a smaller or larger scale
Affects prototypes and performance testing Wrong to assume that all physical effects scale in the same way Some properties scale linearly, whilst others may be exponential E.g. an ant can carry 50x its own weight, but not if scaled up to human
size Complex interactions occur when the number of items increases Computer systems can be affected in a similar way
• Doubling processing power may not double speed
• Doubling users may not halve throughput
• Network performance degrades quickly near its limits
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Signal to Noise Ratio
The ratio of relevant to irrelevant information in a display
Highest possible signal-to-noise ratio is desirable
Signal - relevant data – what we are trying to communicate
Noise – introduced to organise or convey the data, e.g. table borders, shading, gratuitious clip art
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Structural Forms
There are three ways to organise materials to support a load or to contain and protect something
Mass Structures
• Solid structures which rely on mass
• E.g. dams, mountains, pyramids
• Tend to strongly resist failure
Frame Structures
• Internal frame, usually made from triangular sections
• E.g. Eiffel Tower, houses
Shell Structures
• A thin material that contains a volume
• Strength comes from ability to spread loads across the surface
• E.g. eggs, bottles, steam boilers
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Uncertainty Principle
The act of measuring certain sensitive variables in a system can alter them, and confound the accuracy of the measurement
Based on Heisenberg’s uncertainty principle (atomic physics) Two aspects to a measurement
• Sensitivity
– Ease with which a property being measured can be altered
• Invasiveness
– Amount of interference caused by the measurement Examples
• Performance measurement of a computer uses resources
• Voltage measurement draws current & reduces the voltage
• Students adapt to examination techniques to score better
Strive for low invasiveness; sensitivity is predetermined
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Uniform connectedness
Elements that are connected by uniform visual properties are perceived to be more related than elements that are not connected
Elements close to each with similar appearance will automatically group
Human perception will override this if physical connection is shown
Connection lines and shaded areas can group elements
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Visibility
The usability of a system is improved when its status and methods of use are clearly exposed
Systems are more usable when they clearly indicate:
• Their status
• The possible actions that can be performed
• The consequences of those actions
E.g. a red light next to a switch marked ‘Power’
Progressive disclosure on a GUI is an effective tool
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Weakest Link
The deliberate use of a weak element that will fail in order to protect other elements in the system from damage
Examples
• Fuse in a circuit
• Crumple zone in a car
Two types of protection through a weak link
• Passive
– The breakage of the element protects, i.e. a fuse
• Active
– Breakage of the element triggers a response, i.e. a sprinkler system trigger by breakage of a glass bulb
