The Typewriter
Built so one blind woman could write a legible letter.
Read case study →Inclusive design starts from a claim that sounds obvious and turns out to be radical: disability is not a property of a person, it is a mismatch between a person and an environment somebody designed. A building with stairs and no ramp does not accommodate a wheelchair user badly. It excludes them, and it does so because of decisions that could have gone another way at little cost had anyone thought about it early enough.
The practical case is easy to make and worth making. Curb cuts were fought for by wheelchair users and are now used by anyone with a suitcase, a pram or a delivery trolley. Captions were built for deaf viewers and are now switched on in half the world's living rooms. Designing for the edges of a user population tends to improve the product for the middle, which is why "design for extremes" appears here as a strategy rather than an act of charity. Pay particular attention to objective 1.2.2, which admits that inclusive design is not always possible. Being able to say clearly where the limits are and why is a far more sophisticated answer than insisting everything can be made universal. This topic also connects tightly back to the percentile and physiology work in A1.1.
Students must be able toDiscuss how inclusive design requires designing universally accessible products for all users, including those with physical, sensory and cognitive impairments.
Inclusive design (also called universal design, accessible design, or design for all) is an approach that removes barriers and ensures products and environments are usable by everyone, regardless of age, ability, or physical or cognitive difference. The goal is mainstream products that work for all users, not a parallel range of "special needs" versions that stigmatise users and add cost.
The term Universal Design was coined by architect Ron Mace in 1998. The Centre for Universal Design at North Carolina State University defines it as: "the design of products and environments to be usable by all people, to the greatest extent possible, without the need for adaptation or specialised design."
Inclusive design extends User-Centred Design (UCD) by deliberately including community members who might otherwise be overlooked: the elderly, pregnant women, people with disabilities, and those who are temporarily injured. The seven principles of Universal Design are:
- Equitable use: the design is useful and marketable to people with diverse abilities
- Flexibility in use: accommodates a wide range of individual preferences and abilities
- Simple and intuitive use: easy to understand regardless of experience, knowledge, language or concentration level
- Perceptible information: communicates necessary information effectively regardless of ambient conditions or the user's sensory abilities
- Tolerance for error: minimises hazards and adverse consequences of accidental or unintended actions
- Low physical effort: can be used efficiently and comfortably with minimal fatigue
- Size and space for approach and use: appropriate size and space is provided regardless of the user's body size, posture or mobility
Legislation: Many countries legally require designers to consider users with disabilities:
- Americans with Disabilities Act (1990): US federal law covering physical access, employment and product accessibility
- Disability Discrimination Act (1992): Australian legislation requiring reasonable adjustment for people with disabilities
- Similar legislation exists in Canada, South Africa and India
Case Study
Students must be able toDiscuss how the average person correlates to the 50th percentile adult and child, and how it is not always appropriate to design for the average person.
Inclusive design is a goal, not always a guarantee. Two realities place practical limits on how far universal solutions can extend.
The problem with designing for the average: Anthropometric data is reported as percentiles. The 50th percentile is the median: the value below which 50% of the measured population falls. Designing for the "average" person seems logical, but the Union soldiers census of 1850 illustrates the problem: the average height was 5 feet 8 inches, yet it is unlikely that any individual soldier was exactly that height across all relevant body dimensions simultaneously. The statistical average is not a real person.
Body dimensions are not linearly correlated: Someone with short arms does not necessarily have short legs. A person might be 5th percentile in arm reach but 95th percentile in torso height. This means:
- There is no such thing as an "average person" in any practically meaningful sense
- A product designed for the 50th percentile in every dimension will fit very few real people precisely
- Designing for one dimension in isolation can create problems in another
The 5th–95th percentile range: In practice, designers target the central 90% of the population. This means the product must be usable by the smallest plausible user (5th percentile in the critical dimension) and the largest (95th percentile). A seat, for example, needs adjustability to serve both the smallest and tallest users within this range.
Users outside this range (below the 5th or above the 95th percentile) will always require specialist or adapted solutions. This is not a failure of inclusive design but an honest acknowledgement of its practical limits. Designers must identify where the boundary is drawn and be prepared to justify it.
The anthropometric data and percentile method underlying this analysis are introduced in A1.1 Ergonomics.
Students must be able toDiscuss the advantages of designing for extremes when designing products for a general population, and identify where a design for extremes strategy has been used.
When a fully universal solution is not achievable, the design for extremes strategy offers a powerful alternative. Rather than designing for a middle-ground average, designers target users with the most demanding needs: those with physical, sensory or cognitive impairments. The key insight is that solutions developed for extreme users frequently become innovations that benefit the entire population.
This is known as the curb-cut effect: kerb ramps installed for wheelchair users are also used by parents with pushchairs, delivery workers with trolleys, cyclists and people with temporary injuries. The solution built for the hardest case improves the experience for everyone.
Examples from the chapter:
- Oxo Good Grips vegetable peeler: Sam Farber developed the peeler after watching his wife, who had arthritis, struggle to grip a standard peeler. The arthritic hand (the extreme user) required less grip force, a non-slip surface and pressure distributed away from the finger joints. The solution was an oversized handle made from Santoprene (a thermoplastic elastomer) with a scooped-out body and fins for thumb and forefinger, usable with a palm grip rather than a finger grip. The peeler became comfortable for everyone and entered the MoMA permanent collection in 1994. Its principles now appear across the entire Good Grips range and throughout the kitchen tools industry.
- Voice commands and text-to-speech (TTS): Developed for people with visual impairments and dyslexia, TTS reads digital text aloud. The hard constraint (the user cannot read a screen) forced a complete rethinking of human-device interaction. The result is used by millions without any disability for hands-free operation while driving, cooking or multitasking. Virtual assistants (Siri, Google Assistant, Alexa) are mainstream products built entirely on accessibility-driven innovation.
- Tactile pavements: Raised textured surfaces on walkways and platform edges warn visually impaired pedestrians (detectable by cane or foot) that they are approaching a hazard. They also alert any distracted pedestrian nearing a road crossing or platform edge.
- Rumble strips (Audio Tactile Lane Markings): Raised patterns along road edges generate audible and tactile warnings when a tyre crosses them. Designed primarily to alert drowsy or distracted drivers, they provide an additional safety layer for all drivers on long journeys or in adverse weather.
- Braille-like dots on Australian polymer banknotes: Tactile features help visually impaired users identify denominations and benefit all users through a consistent, identifiable surface feature.
Why design for extremes works:
- Hard constraints imposed by extreme users force genuinely new thinking rather than incremental improvement of the status quo
- Solutions that satisfy the most demanding users automatically satisfy less demanding users too
- It future-proofs products: ageing populations, temporary injuries and changing user profiles all shift today's "extreme" toward tomorrow's mainstream
The anthropometric data behind sizing for extreme users, the 5th and 95th percentile ranges, is covered in A1.1 Ergonomics.
Discussion
Find the next curb cut
Every example above, kerb ramps, the OXO peeler, text-to-speech, tactile paving, is now a familiar, well-worn case. That familiarity is a trap: reaching for the same handful of examples in an exam answer signals that you've memorised a list, not that you understand why designing for extremes actually works.
Find your own example: a product or feature originally built for a specific impairment that you or people around you now use without a second thought, and be ready to explain why the extreme constraint, not just a general desire to be inclusive, forced a better design. Then find a counter-example: a case where designing for an extreme user made the product worse for everyone else, or where a company bolted on an "accessibility feature" that didn't actually solve the real problem. What separates the two?
Ten questions covering Universal Design principles, percentile ranges, legislation and the design for extremes strategy. Select one answer per question, then click "Check all answers" to see your score and the explanations.
Q1 · 1.2.1 Universal Design
Which statement best captures what universal design asks of a product?
Universal design targets the widest possible audience in a single mainstream product, regardless of age or ability. The standard definition is design usable by all people to the greatest extent possible without needing adaptation. A separate adapted version fails that test twice over, since it stigmatises the people who need it and adds the cost of a second product line.
Q2 · 1.2.1 Universal Design
Which principle of universal design requires that necessary information reaches the user regardless of ambient conditions or their sensory abilities?
Perceptible information is the principle behind repeating a message across more than one sensory channel, such as pairing a warning colour with a symbol or a sound with a vibration. Equitable use concerns whether the design serves diverse abilities without singling anyone out, and low physical effort concerns fatigue during use.
Q3 · 1.2.1 Universal Design
Inclusive design aims at mainstream products rather than a separate range of "special needs" versions mainly because separate versions:
A parallel product line marks its users out as different and is usually more expensive, because it is made in far smaller volumes. The goal is one product that works for everyone, which is why inclusive design extends user-centred design by deliberately including people who are otherwise overlooked: older users, pregnant women, disabled people and the temporarily injured.
Q4 · 1.2.1 Universal Design
Accessibility legislation exists in many countries and shapes what a designer must consider. What does such legislation typically require?
The Americans with Disabilities Act 1990, the Disability Discrimination Act 1992 in Australia and the Equality Act 2010 in the UK differ in detail, but all turn on reasonable provision rather than a guarantee of universal usability. For a designer this sets a floor, not a target: meeting the legal minimum is not the same as designing inclusively, and the wider percentile question still has to be answered.
Q5 · 1.2.2 Designing for Percentiles
Why is there no meaningfully "average" person to design for?
Someone can be 5th percentile in arm reach and 95th percentile in torso height at the same time. The Union soldiers census of 1850 makes the point: the average height was five feet eight inches, but no individual soldier was average across every relevant dimension at once. A product built to the 50th percentile in every dimension therefore fits almost nobody precisely.
Q6 · 1.2.2 Designing for Percentiles
Which percentile range do designers normally target?
This range covers the central 90% of the population, so the product must work for the smallest plausible user in the critical dimension and for the largest. A seat, for example, needs adjustment to serve both ends of that band rather than a single fixed setting.
Q7 · 1.2.2 Designing for Percentiles
Which statement about the limits of inclusive design is most accurate?
Naming the limit is a more sophisticated answer than claiming everything can be made universal. Excluding the outermost 5% at each end is a deliberate compromise, not an oversight, and stating where the line is drawn and why is what an examiner is looking for.
Q8 · 1.2.3 Design for Extremes
Text-to-speech and voice control were developed for users who could not read a screen, and are now used by millions of people while driving or cooking. This illustrates:
The constraint could not be met by enlarging or brightening text, so it forced a different interaction model entirely. That is the structural reason the strategy works: a hard constraint prevents incremental tinkering with the status quo. Kerb ramps, built for wheelchair users and now used with prams, suitcases and trolleys, gave the effect its name.
Q9 · 1.2.3 Design for Extremes
A vegetable peeler is developed around the constraint that its users have arthritis. Which set of features does that constraint demand, and what is the wider effect?
Arthritis rules out the thin smooth metal handle entirely and forces an oversized soft handle worked with a palm grip rather than a pinch. The resulting tool is easier for everyone, which is the design for extremes argument: a constraint that looks narrow produces a solution the general population prefers. OXO Good Grips is the standard example, and it reshaped the whole kitchen tools market.
Q10 · 1.2.3 Design for Extremes
A writing machine is built for a single blind user so that they can produce letters legible to sighted readers, with no market in mind. Its mechanism later becomes standard office equipment. This sequence supports the argument that:
The constraint was absolute: the user could not check the page, so the mechanism had to place characters reliably without sight. Solving that produced the typewriter, and carbon paper arrived as a by-product of needing to transfer ink consistently. Designing at the edge of the population removes the compromises that a comfortable average user would have tolerated, and the result is usually better for everyone.
Paper 2 structured questions require extended written responses. Use the sample answers and mark scheme notes to practise and self-assess.
Question 1 · 4 marks
Explain the difference between designing for the 50th percentile and designing for the 5th–95th percentile range. Why is designing for the average often inappropriate for inclusive design?
Show example answer
Designing for the 50th percentile means basing a product on the median value of a specific body dimension: the point below which 50% of the population falls. Designing for the 5th–95th percentile range means accommodating the central 90% of the population, from the smallest 5th percentile up to the largest 95th percentile.
Designing for the average is often inappropriate because body dimensions are not linearly correlated. Someone with short arms does not necessarily have short legs: a person might be 5th percentile in arm reach but 95th percentile in torso height. The Union soldiers census (1850) illustrates this: the average height was 5 feet 8 inches, yet it is unlikely any individual soldier was exactly that height simultaneously across all relevant body dimensions. The statistical average describes no real person precisely.
A desk designed for 50th percentile elbow height will cause a short user to reach up (shoulder strain) and a tall user to bend down (back pain). Only by designing across the full 5th–95th range (for example through adjustability) can a product serve the realistic breadth of users it will encounter.
Question 2 · 6 marks
Describe three different examples of inclusive design from the chapter. For each example, explain which user group it primarily assists and how it also benefits the general population.
Show example answer
1. Oxo Good Grips vegetable peeler: Inspired by Sam Farber observing his wife with arthritis struggling to hold a standard peeler. The large Santoprene handle with scooped-out body and fins requires only a light palm grip. Primary user group: People with arthritis or reduced hand strength. Benefit to general population: The comfortable, non-slip handle reduces hand strain and fatigue for all users, making the task easier regardless of whether the user has any impairment.
2. Voice commands and text-to-speech (TTS): Reads digital text aloud, allowing access to information without requiring the ability to see a screen. Primary user group: People with visual impairments or dyslexia. Benefit to general population: Enables hands-free operation while driving, cooking or exercising. Virtual assistants like Siri and Google Assistant (used by millions without any disability) are built directly on this accessibility-driven innovation.
3. Rumble strips (Audio Tactile Lane Markings): Raised patterns along road edges generate audible and tactile feedback when a tyre crosses them. Primary user group: Drowsy or distracted drivers at risk of drifting off the road. Benefit to general population: All drivers receive the warning, providing an additional safety layer on long journeys or in poor weather conditions, protecting passengers, pedestrians and other vehicles as well.
Question 3 · 5 marks
Evaluate the role of anthropometric data in inclusive design. Why must designers go beyond simple averages and percentiles to create truly inclusive products?
Show example answer
Anthropometric data (systematic measurements of human body dimensions) provides the quantitative foundation for inclusive design. It enables designers to understand the range of human sizes and proportions, set dimension targets for product features, and specify adjustability ranges that serve a defined population breadth.
However, anthropometric data alone is insufficient for the following reasons:
1. Non-linear correlation: Body dimensions do not correlate linearly. A person who is 5th percentile in arm reach may be 95th percentile in torso height. Designing for one dimension in isolation creates problems in another. The Union soldiers example shows the gap between statistical averages and real individuals.
2. No average person: Optimising for the 50th percentile in every dimension produces a product that fits no real user precisely, because no individual is simultaneously average in all dimensions.
3. Beyond physical dimensions: Inclusive design must also address sensory impairments (vision, hearing), cognitive differences (dyslexia, memory impairment) and temporary conditions (injury, pregnancy). Anthropometric tables capture none of these.
4. Static versus dynamic use: Anthropometric data records static measurements (e.g., standing height), but products are used through dynamic movements: reaching, bending, twisting. A dimension that falls within the target range statically may cause strain during realistic use.
Truly inclusive design combines anthropometric data with qualitative user research, observation and iterative testing with diverse users including those at the 5th and 95th percentile extremes and people with various impairments.
Question 4 · 4 marks
Outline the ethical implications of excluding users with cognitive impairments from mainstream product design. Refer to the chapter's discussion of inclusive design principles.
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Discrimination and legal violation: Many countries require consideration of people with disabilities by law (including cognitive impairments) through legislation such as the Americans with Disabilities Act (1990) and Australia's Disability Discrimination Act (1992). Excluding these users violates the Universal Design principle of equitable use and may constitute a legal breach in regulated markets.
Loss of autonomy: When mainstream products are unusable by people with cognitive impairments (such as those with memory loss, dyslexia or intellectual disabilities), those individuals become dependent on others for everyday tasks. Inclusive design aims to enable independent use for as many people as possible, reducing this dependency.
Missed innovation: designing for cognitively challenged users drives innovations that benefit everyone. Text-to-speech technology, developed for users with visual and cognitive impairments, now enables hands-free operation for the entire population. Excluding cognitive impairments from the design brief forfeits these wider benefits.
Social exclusion: When mainstream products are inaccessible, users with cognitive impairments are pushed toward specialised, stigmatising and often more expensive alternatives. The Universal Design principles of simple and intuitive use and tolerance for error directly address cognitive accessibility and should be applied from the start of the design process, not retrofitted afterward.
Question 5 · 6 marks
Analyse how the "design for extremes" strategy leads to more innovative and future-proof designs. Use the Oxo Good Grips peeler and one other example from the chapter to support your analysis.
Show example answer
The design for extremes strategy develops solutions for users with the most challenging needs: those with physical, sensory or cognitive impairments. Counterintuitively, designing for these extreme users consistently produces innovations that benefit the broader population. This is the curb-cut effect: a feature built for the hardest case improves the experience for everyone.
Example 1 (Oxo Good Grips peeler): The extreme user (a person with arthritis) required a handle needing minimal grip force, a non-slip surface and pressure distributed away from the finger joints. These constraints ruled out the thin, smooth metal handle of a standard peeler entirely. The solution (an oversized Santoprene handle with scooped body and fins, usable with a palm grip) eliminated hand fatigue for all users, not just those with arthritis. It entered MoMA's permanent collection in 1994, demonstrating that accessibility constraints produced a design of broader cultural significance. The same principle is now found throughout kitchen tools, garden tools and writing instruments. Innovation driver: the hard constraint, not incremental market research.
Example 2 (Voice commands / TTS): The extreme user (visually impaired; cannot interact via screen) forced a complete rethinking of how people interact with devices: from visual and touch-based to voice. The constraint could not be solved by making text larger or brighter. The result (natural-language voice interaction) is now used by hundreds of millions of people without any disability, as the primary interface for virtual assistants and smart speakers. Future-proofing dimension: as driving, exercise and multitasking become more common contexts for device use, the hands-free affordance originally designed for disability becomes increasingly relevant to the mainstream.
Why the strategy works structurally: Extreme constraints prevent designers from defaulting to incremental improvement of the status quo. Solutions must be fundamentally different. Because physical, sensory and cognitive needs exist on a spectrum (and because ageing populations, temporary injuries and changing environments continuously expand the population with those needs), a product designed for today's extreme serves tomorrow's mainstream. Design for extremes is not social responsibility as a trade-off against innovation; it is the mechanism that produces innovation.
The 7 principles of universal design
universaldesign.ie/about-universal-design/the-7-pri…
Each principle with its guidelines and examples. This is the framework 1.2.1 is built on, so read the guidelines under each principle rather than the headline alone.
Good Grips Peeler, Smart Design, MoMA collection
moma.org/collection/works/3758
The museum record for the peeler, including how Sam Farber came to commission it after watching his wife struggle with arthritis. A design for one group of users that turned out to be better for everyone.
The curb-cut effect, Stanford Social Innovation Review
ssir.org/articles/entry/the_curb_cut_effect
The full argument for why designing for people with disabilities produces benefits far beyond them, with the history of how curb cuts were won. The strongest single source for 1.2.1.
Americans with Disabilities Act
ada.gov
The 1990 legislation and its accessibility design standards. Useful for seeing accessibility written as measurable requirements rather than intentions.
Inclusive design, Nielsen Norman Group
nngroup.com/articles/inclusive-design
Sorts out inclusive design, universal design and accessibility, which are used loosely and mean different things. Read it before you use the terms in an exam answer.
Disability, World Health Organization
who.int/news-room/fact-sheets/detail/disability-and…
Global prevalence figures for disability. The numbers are the argument that inclusive design is a mainstream requirement, not a niche one.
Tactile feature on Australian banknotes, Reserve Bank of Australia
banknotes.rba.gov.au/australias-banknotes/next-gene…
Why the raised bumps exist, how the vision impaired community shaped them, and why the number of bumps changes with denomination. Note that it is deliberately not Braille.
Linking Questions
- To what extent is a deep understanding of ergonomics important when engaging with inclusive design? (A1.1)
- To what extent can designers remove personal bias when using user-centred research methods? (A2.1)
- How can products integrate mechanical systems to improve accessibility and usability in an inclusive design approach? (A3.3) (B3.3)
- To what extent can the inclusion of electronic systems in products enhance accessibility and usability for all end-users? (A3.4) (B3.4)
- Which aspects of inclusive design benefit from the designer going beyond usability when designing products? (C1.3)
- How important is accessibility and usability when conducting product analysis and evaluation? (C3.1)
Case Study: The Typewriter
Around 1808, an Italian inventor named Pellegrino Turri built a writing machine for a close friend, Countess Carolina Fantoni da Fivizzano. She had lost her sight and could no longer write a letter anyone else could read. There was no real market for it, just a goal to help someone who couldn't see write letters without help. Several of the Countess's letters, typed on Turri's machine, survive today. Unfortunately the machine itself has been lost to history.
Turri's solution needed a way to check that the ink had actually transferred to the page, so he is also credited with inventing carbon paper specifically to make his machine work. Six decades later, a commercially successful version by Christopher Sholes introduced the QWERTY key layout, and the typewriter went on to dominate offices worldwide for over a century. Every keyboard in front of a sighted, able-bodied typist today, including the one this text was written on, descends from a machine built to solve one blind woman's very particular problem.
Learn more about the history of the keyboard: History-Computer.com