<aside> š© To design for humans means aligning your design with the actual HF capabilities of those users. Designers must determine the capabilities of users before they design an intervention for them.
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Every product putsĀ demandsĀ on its usersā vision, hearing, strength, etc. If those demands exceed the users'Ā capabilities, then those users will not be able to use the product, or will not use it well, or will not enjoy using it, or may be injured or even killed by it.
In principle, the wider the range of HFs for a particular intervention, the larger its potential market. However, this typically results in more complex products, which in turn increases costs and decreases durability and reliability. On the other hand, a small range of HFs can allow the design of cost effective, efficient, and reliable interventions; however, this reduces the range of users who can use it because such designs typically exclude and marginalize users who are āfar from averageā.
One must therefore seek to balance the ranges of HFs to maximize the range of potential users while also making a product that is reasonably reliable, cost-effective, and efficient.
It doesnāt matter if you create a truly āuniversalā design that costs so much that only a handful of people can afford it. Nonetheless, there is a growing expectation that designing for the broadest possible range of user is essential for both corporate social responsibility and financial success.
Thus, one must study human capabilities to set appropriate ranges of design HFs, to design a product that is both usable and functional.
Furthermore, not all possible HFs are relevant in a specific project. Thus, one must prioritize those HFs that are most relevant to the scope of a given Design Brief.
<aside> š” Example 1:Ā Night vision devicesĀ are predicated on users having some minimal amount of vision; users who are completely blind areĀ excluded by definitionĀ from this class of product. Sometimes, this kind of exclusion is unavoidable, but the rationale for such exclusions should be clear, well-documented, and not founded on biases or discriminatory principles.
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<aside> š” Example 2:Ā Both surgical clamps and locking pliers provide the same basicĀ function, but you wouldn't want your surgeon operating on you with pliers. The difference is the scope and context in which the required function is to be implementedĀ and the capabilities of the users in each case.
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We refer to the overall scope of all HF ranges as the HFĀ envelopeĀ for a product.
AĀ HF capabilityĀ is the natural limit of a user's vision, hearing, or any other HF, beyond which the user cannot use a product.
For example, if an intervention requires a user to lift a 20 kg weight from ground level, but the user cannot lift more than 15 kg from ground level, then the interventionās demand (20 kg lifting) has exceeded the user's capability (15 kg lifting). This means the intervention excludes anyone who cannot lift 20 kg safely.
To design a good intervention, designers must first consider the capabilities of their target users for all relevant HFs, then use those capabilities to guide development of the engineering Requirements which in turn define the scope of performance of any suitable intervention.
Since no two people are exactly alike, working with HF capabilities is a statistical task. Designers consider a population of users and the statistical distribution of capability across that population. The goal then becomes determining a level of capability that will statistically inconvenience or harm theĀ fewestĀ possible members of a population.
In most general terms, one determines the demands placed on HF capabilities by a product or design as follows: