AI made the second bar twice as long. Did the value really double?

Read the axis start and the data labels. A cropped bar-chart axis can make a modest numerical gap look much larger.

ONS guidance recommends starting bar and area chart axes at zero because lengths or areas represent values. It distinguishes line and scatter charts, whose axes can be cropped where appropriate. “Every chart must start at zero” is not the same rule.

The same invented values, two scales

Our example values are A=90 and B=100 arbitrary units. Starting at zero gives proportional lengths 90 and 100. Starting at80 gives visible spans10 and20: B’s visible bar is twice A’s, although100 is not twice90. We calculated the spans and drew the comparison ourselves.

Ask for the scale before interpreting the claim

Suggested input: “Keep the original values and units. Use a zero baseline for this bar chart, label both values and state the axis limits. Do not infer a percentage increase from cropped bar lengths.” Confirm the exported chart’s axis as well as the accompanying prose.

Use the values for the numerical comparison

For these fictional numbers, the gap is10 units and the increase from90 is about11.11%, not100%. We checked the arithmetic. These values are not sales, model scores or measured performance.

Choose a chart for the intended question

If a close trend is hard to see with bars, consider a clearly labeled line or dot chart appropriate to the data. Do not hide the baseline choice. Our recommendation is to provide the underlying values so the reader can check the visual impression.

Published October 14, 2026. Only invented arithmetic and our own bilingual SVG comparison were checked. We did not test a chart-generating AI, spreadsheet editor or the effect on readers.

Sources: ONS · Chart axes.