In 2006, while I was product manager at the fictional Cervellan Homewares, I approved a perspective-only instruction drawing for a flat-pack stool. During an observed exercise, thirty of forty-eight participants completed the sample assembly while eighteen reversed a cross brace. I had treated the drawing as self-explanatory because I already knew how the parts belonged together. Owen Calverden watched the task and challenged my suggestion that printing the same image larger would be enough. The problem concerned interpretation of orientation and sequence, not simply the size of the illustration.
I wanted to keep the existing artwork and the development timetable. Owen argued that the instruction needed to show the decision a first-time assembler actually faced. We returned to the point where the brace could be read in two ways and changed the orientation shown in the sequence. We added part labels and examined how the reader would move from one step to the next. A$280000 supported the illustration and instructional-development work. I accepted the extra work rather than asking a general caution at the end to repair a confusing choice earlier in the process.
The retest used forty different participants. Thirty-four completed the sample assembly and six needed assistance. Those results were useful, but they did not prove that the new sequence worked unaided for everyone. The different groups also made it inappropriate to present a precise population improvement from a simple subtraction. Quality and engineering colleagues retained responsibility for the assessments within their remit. Neither exercise was described as a safety certification, and the case asserts no injury, recall or regulatory finding.
The mistake was mine: I had approved an account of the task that relied on knowledge the reader did not yet possess. The correction required me to withdraw that assumption in front of colleagues who had acted on it. I could preserve the useful product-development work without defending the original drawing. The consequence was a revised sequence with an explicitly unresolved assistance group. Since then, I have wanted instruction reviews to show what a person does at the confusing step, rather than rely on the confidence of people who already know the answer.