The task and original case
Compare two chart treatments for values 99 and 100, while keeping the arithmetic separate from their visual appearance. The portfolio output should explain what the axis changes and why a small numerical difference can appear visually dramatic.
| Case element | Value or requirement |
|---|---|
| Inputs | Values 99 and 100 are shown with a vertical axis starting at 98. |
| Build | Two chart treatments and a caption explaining the honest comparison. |
This is an original invented exercise. It is independent practice, with no employer assessment or open-vacancy claim. Download the inputs, attempt your own result, then open the separate answer key.
Data and worked inputs
Build a result another person can follow
Create a table with the two values and compute the absolute difference and relative change from 99. Then draw one bar chart beginning at zero and another beginning at 98, with visible axis labels. Use the same data, dimensions and category labels so the only deliberate difference is axis treatment.
Include a readable data table or equivalent values alongside the chart. W3C's table guidance supports meaningful header relationships for that tabular alternative. Explain any truncated axis in the caption. Do not let a chart's bar-height ratio substitute for the underlying-value calculation; under the truncated axis, the visible bars rise one and two units above 98.
Sources[1]
Check the worked result
Absolute increase is one unit. Relative increase is 1 ÷99, approximately 1.01%. In the chart starting at 98, the visible bar segments have heights one and two, so the second looks twice as tall. The underlying value did not double.
The zero-baseline view makes the near-equality clear. A truncated-axis view can highlight small variation when clearly disclosed and appropriate to the chart form, but your report must preserve the values and explain the comparison rather than relying on dramatic appearance.
Make the failure visible
Remove the axis labels from the truncated chart and ask whether its message remains interpretable. Test a chart exported at a narrow width and ensure labels and the data alternative remain usable. Also change the baseline value to zero: relative change from zero is undefined under this formula, so it needs a separate description.
Revise it and ask someone to reproduce it
Ask a peer to state the absolute and relative change before you reveal the chart captions. If their answer is “100% increase,” inspect what the visual led them to assume. Revise the treatment and repeat the reading check. Preserve both charts and the feedback as evidence of the design decision.
- The caption names the axis treatment and underlying values.
- One-unit and approximately 1.01% changes remain distinct from bar appearance.
- The chart has an understandable labelled data alternative.
Describe the work accurately
After completing your own version, you could adapt this project bullet: “Built an independent chart-interpretation exercise comparing axis treatments with explicit absolute and relative change and a readable data alternative.”
Use Projects or Independent practice as the heading. Keep the input files, result and revision together. Describe only your own completed work; the invented numbers are model outputs, not employer results or measured business impact.