Simple Bar Charts — Revision Notes

⚡ 30-Second Revision

Revision checked 17 October 2026.

Read unit and zero baseline.
Difference, ratio and percentage increase are distinct.
Common scale cancels in ratios only.
Combined rates need combined denominators.
Visits do not equal unique visitors.

2-Minute Revision

For bars 30, 45, 60 and 75, the total is 210 and mean 52.5. The last bar is 2.5 times the first, but exceeds it by 150 percent. A truncated axis changes visual impression, not the labelled arithmetic. If four categories average 25, their total is 100 even when only three bars are known. Always preserve the category and measurement unit.

5-Minute Revision

Original drill: Centres P, Q and R record 40, 60 and 100 visits. Total visits are 200; Q represents 30 percent; R exceeds P by 150 percent. These results do not identify unique visitors or service quality.

Change the axis to hundreds of visits: the share and percentage comparison remain the same, while the total becomes 20,000 visits. Finally, suppose the centres serve unequal populations. The visit ranking alone cannot establish a per-resident ranking.

This sequence tests scale, denominator and inference separately.

Vyyuha Quick Recall

BARS: Baseline; Axis units; Reference denominator; Scope of the measure.