Write a design specification as a list of clear, measurable requirements drawn from research, and use it to guide and later test the design

What this dot point is asking

SEAB wants you to write a design specification, which is a list of clear, measurable requirements that your product must meet. The specification grows out of your research and the brief, and at the end of the project it becomes the checklist you test the product against. The key skill is making each point checkable, not vague.

The answer

What a specification is

A specification is a numbered list of requirements. Where the brief is a short headline, the specification is the detail. Each point should be measurable or checkable, so that later you can clearly say whether the product meets it.

What the points should cover

A balanced specification covers several areas. A useful checklist is:

• Function. What the product must do, with numbers where possible (for example, hold at least 15 books).
• Size. Maximum or minimum dimensions to suit the user and space.
• Materials. The kind of material needed, linked to a property such as durability.
• Safety. Requirements such as no sharp edges, stable when loaded.
• Cost. A budget the product must come in under.
• Appearance. A clear standard, for example a colour to match the room or a labelled area.

Making points measurable

The difference between a weak and a strong specification is measurability. "It must be strong" is an opinion. "It must support a 5 kg load without bending" can be tested. Where you cannot use a number, use a clear yes or no test, such as "it must have rounded corners".

How the specification is used

The specification works at both ends of the project. During design it guides your ideas and stops you wandering off the task. At the end it becomes the evaluation checklist: you test the product against each point and record pass or fail. This is why measurable points matter, because they give a clear result instead of a guess.

Examples in context

Example 1. A bird feeder. Research shows the birds in the garden and the food they eat. The specification then includes measurable points such as "must hold at least 200 g of seed", "must keep seed dry in rain", and "must be no wider than 200 mm to hang from a thin branch". Each can be tested later.

Example 2. A weak point exposed. A student writes "must be easy to clean" with no detail, then cannot test it. Rewriting it as "must come apart into two parts without tools so it can be washed" turns an opinion into a checkable requirement.

Try this

Q1. State three areas a design specification should cover. [3 marks]

• Cue. Any three of function, size, materials, safety, cost, appearance.

Q2. Turn this vague point into a measurable one: "The stool must be the right height." [2 marks]

• Cue. Give a number, for example "The stool seat must be 450 mm above the floor to suit a standard desk."

Q3. Explain why measurable points make evaluation easier at the end of a project. [3 marks]

• Cue. Because you can take a measurement or run a simple test and record a clear pass or fail for each point, rather than relying on opinion.