Choose charts that preserve the comparison

Understand the method

A chart should answer a specific question more quickly than a list of numbers while retaining enough detail to check the claim. Decide what is being compared before selecting a visual. In this module, monthly completed value compares totals, while channel AOV compares a ratio across groups. They require different labels and denominators even if both use horizontal bars.

Compare totals on a meaningful baseline

A simple bar comparison can show April’s €2,900 and May’s €3,420 completed-order values. Bar length encodes magnitude, so start the value scale at zero. Truncating the baseline near €2,800 would exaggerate a €520 difference. Put exact values beside the bars and identify EUR as the unit. A reader should not need to estimate the amount from colour or bar length alone.

The worked example adjusts the bar-length scale to the currently displayed values and says so. This keeps a single-month view usable, but it means a bar’s pixel length must not be compared across screenshots with different filters. The labels carry the exact numbers. If your design asks readers to compare several panels or exported views directly, use a shared fixed scale and document it instead of independently stretching each chart.

Show a ratio with its contributing count

For May, web AOV is €90 from two completed orders, and store AOV is €180 from 18. For April, web AOV is €100 from 18 and store AOV is €550 from two. Include these counts beside the values. A high mean based on two orders, one of them €1,000, has a different interpretation from a similar mean supported by a large and stable group.

Overall AOV is weighted by completed-order counts. April is 90% web and 10% store, producing €145. May is 10% web and 90% store, producing €171. An equal mean of the channel means would instead be €325 and €135, answering a hypothetical equal-mix question. Do not present those scenario values as the actual headline AOV. The channel chart should help readers discover that distinction.

Keep visual complexity proportionate

Two supplied months do not establish a seasonal trend. A line chart can connect the values, but a smoothed curve or a forecast extension would imply structure that the fixture does not support. A pie chart is also a poor substitute for showing changing channel AOV and counts: it focuses on parts of a whole rather than the numerical comparison being explained. Choose the simplest visual that makes the question and denominator clear.

Make the result available without colour

Use readable labels, units and an adjacent numerical table or text summary. Teal and lavender distinguish series in the course design, but category names and exact values must remain explicit. For charts delivered as images, provide a description that conveys the useful comparison, not merely “chart.” For an interactive page, ensure the same evidence remains available in ordinary text and tables. Do not claim an accessibility certification from a visual inspection alone.

Finally, verify the chart’s source population against the headline calculation. A beautiful chart can still include returned orders or use an unweighted mean. The visual is part of the calculation chain, so its filters, labels and source bindings deserve the same checks as the summary table.