Analysis of Function: how to evaluate fitness for purpose

When completing a high school design project, students commonly evaluate the function of a design. This means you must analyze how well a product does its job and meets the original design problem or need. In other words, you must evaluate its fitness for purpose in its broadest sense, and identify how successfully it works from a practical perspective. Analysis of function involves a careful investigation of what the product does and whether it does this well.

Products are designed and made because of their functions. To design a product is to conceive of the use of the product and to find a suitable geometrical and physio-chemical form for the product and its parts, so that the intended function, or functions, can be fulfilled.

– David Jensen, Introduction to Mechanical Design and Manufacturing, quoting Dr Jaap Daalhuizen, Delft Design Approach, Delft University of Technology (2018)

For example, the function of a cup is to hold liquid for drinking; the function of a refrigerator is to cool foods and drinks; the function of a poster is to communicate a message; the function of a road sign is to provide navigation or safety information. These examples illustrate that function can range from purely practical considerations (such as a cup holding liquid) to psychological or even symbolic purposes (such as a wedding ring representing commitment). Of course, a single product may have multiple functions.

When evaluating the function of a product, it helps to look beyond surface-level appearance and actually test and use the item (conducting primary research). This might involve assessing how a product performs in various circumstances or environmental conditions, with a range of different users.

You may also conduct secondary research. This might involve gathering feedback from online forums (such as reading product reviews on Amazon or other online reviews about the product). These secondary sources can be quoted and referenced as necessary.

While carrying out testing and evaluation, it is helpful to identify strengths or weaknesses in functional capabilities, suggesting improvements where appropriate. You should consider a range of relevant factors, analysing different aspects of functionality.

The following starting points may help with this task (please note that not all of these questions are appropriate for every product):

• What does the product do? What is its primary function or purpose? Does it have any other functions? How does it achieve this? How might I test this capability?
• Adaptability and versatility: Can it be used for multiple functions – including those it was not intended for? Is it useful for a range of different tasks or contexts? Does it have additional functions beyond its original or primary purpose?
• Efficiency/speed of use: How quickly does the product complete its tasks? Are there any unnecessary steps or complications in the use of the product? Does it achieve its goal slowly in a way that is impractical? Are there any delays or bottlenecks in its functionality?
• Strength and resilience: How strong and robust is the product? Does the product have specific structural features that ensure it is strong enough for the task intended? For example, does it utilise triangular frames to increase rigidity, or reinforcing elements such as gussets, ribs, braces or laminating? Is it subjected to heavy compression forces?
• Ease of operation: Is the product intuitive to use and user friendly? Does it require complex instructions? Is it logical or confusing to use? What is the learning curve for understanding and using the product? Are the controls and interface clear and straightforward? (You may wish to link this discussion to the principles of ‘good’ design posed by Dieter Rams.)
• Reliability and consistency: Does it always work as intended? Can it be depended on? Does the product sometimes fail or generate unreliable outcomes?
• Compatibility: Does it integrate well with other existing systems or tools? How well can the product connect or interface with other systems? Has it become outdated in any way? Are there constraints in its ability to work with other components, products, or technologies? Does it require special adaptors, accessories, or modifications to function or connect?
• Movement and flexibility: Are there any issues with moving parts, junctions, joints, or connections between different pieces of the product? Do moving parts, such as hinges, levers, linkages, belts, pulleys, and gears move smoothly? Are any parts in tension, bending, or subjected to turning or rotational forces?
• Lines of sight / vision-related concerns: Is vision obscured? Does this hinder operation of the product? Does glare off any surfaces interfere with use of the product?
• Use of space: Are there any issues with transitions between spaces or separate parts of the product; such as adjoining spaces; indoor/outdoor transitions etc.
• Legibility/readability: Can written elements or symbols be understood? Do they communicate information clearly? How effectively does the product transmit information?
• Environmental conditions: Does the product need to operate in a range of different environmental conditions (inside / outside / in the rain etc) and does this effect the use of the product? Is usage limited in different scenarios? Does its performance change or degrade in different circumstances?
• Safety concerns: Does use of the product lead to any injuries or harm?
• Scalability: Can the product handle increased workload or expanded use? Does its performance change with increased demand? Are there limitations to its capacity? How consistent is the product’s performance over time? Does its performance degrade with repeated use?
• Precision and accuracy: How precise are the product’s outputs or actions? What is the margin of error in its performance? Can it achieve the required level of accuracy for its intended purpose?
• Feedback signals: Does the product provide feedback signals to the user while in use? Does it communicate its current state or progress effectively?
• Mechanical Capacity: What is the product’s maximum capacity for its intended function? Are there clear limits to its operational capabilities? How does it perform when pushed to its maximum potential? (You may wish to discuss whether destructive and non-destructive testing is appropriate in this circumstance.)
• Changing customer requirements: Have the needs of the user changed with time and does this effect the current functioning of the product?
• Future concerns: Do you identify any future circumstances where the product may no longer function as intended? Has is begun to degrade? It showing signs of age or wear and tear? Are these expected, given the lifespan of the product?

Some functional considerations, such as those relating to the size and weight of a product, might be discussed in more detail when considering ergonomics.

Note: Our article about testing and evaluation provides examples of how you might go about testing the function of a particular product.