Fig. 13 shows anthropometric data being used to design a school desk. The item shown is commonly used in design and technology projects. It has been designe...

(a) Anthropometrics is the collection and study of measurements of the human body. [1] These measurements (such as height, arm length, seated shoulder height, hand span, and leg length) are gathered from large populations and used by designers to ensure products and environments fit the physical dimensions of the intended users.

(b) The body measurement labelled A is the popliteal height (the height from the floor to the underside of the thigh just behind the knee when seated). [1]

This measurement is critical when designing desk and chair heights. The seat height should match the popliteal height so the user's feet rest flat on the floor. Combined with the seated elbow height, it determines where the desk surface should be positioned so the student can write comfortably with forearms roughly parallel to the floor.

(c) Why designers use the 5th to 95th percentile range rather than the average: [2]

Designing for only the average (50th percentile) user would mean the product is comfortable for a narrow band of people around the middle of the size distribution but too small for larger users and too large for smaller users. A significant proportion of the population would find the product uncomfortable or unusable. [1]

By designing for the 5th to 95th percentile range, the product accommodates approximately 90% of the intended user population. This practical range balances inclusivity against the cost and complexity of making a product that fits absolutely everyone. The extremes at the 1st-4th and 96th-99th percentiles may require specialist or adjustable solutions. [1]