Create an honest chart specification
How does an axis floor change the apparent size of a difference?
Entering midway? Revisit Build a brief from evidence for the preceding worked example, or start here and use the explanation below.
Start with a concrete question
Two observed quantities, 92 and 96, can be encoded as bars or points. Inspect geometry, then specify or sketch your own chart.
Try the initial inputs, then write a prediction before changing one setting. All calculations run locally on your CPU.
What do you expect?
Before changing a setting: How does an axis floor change the apparent size of a difference? Write what you expect and why.
Change one thing. Inspect what happens.
- Calculate the absolute difference before changing the chart range.
- Compare the displayed height ratio at floors 0 and 90.
- Choose bars or points and justify the visible range.
- Draft a caption naming values, units, denominator and limitation.
Your settingsMechanism
Calculation belowEvidence
Compare outcomes
Compare the current results
Every bar starts at zero and uses the same numeric scale in this chart. The upper bound automatically adjusts to the largest current value (at least 1), so compare the numbers when changing inputs. Units and quantities come from each label; different kinds of quantity are not interchangeable. Displayed values are rounded to at most six significant digits.A = 92 units; B = 96 units. Difference = 4 units, or about 4.35% relative to A.
Follow the calculation
- Original observations: A=92, B=96; top axis=100; lower axis=0.
- Displayed bar height: A=92, B=96.
- True relative increase: 4/92 × 100 = 4.35%.
- Bars encode quantity by length. A truncated baseline makes length ratios differ from value ratios.
Choose a chart encoding that matches the claim, keep labels visible, and state the absolute difference alongside any relative change.
Author a chart specification and caption
Specify marks, axis bounds, units and labels for A=92 and B=96. Write a caption that gives the absolute difference without confusing displayed bar lengths with value ratios.
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Compare with my earlier draft
Chart title: B is three times A! Bars start at 90. Caption: B is much better.
Explain what you changed and why in your observation notes. Text differences do not establish quality.
Inspect an example solution after your attempt
Use bars from 0 to 100 with values 92 and 96 labeled, or clearly labeled points on a narrower axis. Caption: B exceeds A by 4 units, about 4.35% relative to A. These are two observations; uncertainty and usefulness are not supplied.
This is one worked example. Test another input and explain its limitations.
Captures keep your inputs, prediction and observation. Results are recalculated from those inputs. Resetting inputs keeps your captures and challenge history.
Explain the mechanism
Create an honest chart specification
Two observed quantities, 92 and 96, can be encoded as bars or points. Inspect geometry, then specify or sketch your own chart.
Follow the mechanism
The absolute difference is four units regardless of axis choices.
With a floor of 90, heights become 2 and 6, giving a misleading three-to-one bar-length ratio.
A point plot can emphasize small differences with a clearly labeled narrow range; it does not change the underlying values.
Worked example
Original observations: A=92, B=96; top axis=100; lower axis=0.
Displayed bar height: A=92, B=96.
True relative increase: 4/92 × 100 = 4.35%.
Bars encode quantity by length. A truncated baseline makes length ratios differ from value ratios.
Calculation
Displayed height = value − axis floor; height ratio = (96 − floor)/(92 − floor).
Try a controlled comparison
Calculate the absolute difference before changing the chart range.
Compare the displayed height ratio at floors 0 and 90.
Choose bars or points and justify the visible range.
Draft a caption naming values, units, denominator and limitation.
What this does not establish
- All messages, people, documents and outcomes here are original fictional teaching fixtures; results are not measurements of real organizations.
Try a fresh case
Values 52 and 56 are drawn as bars from a floor of 50. What is the second-to-first bar-height ratio?
This is a public practice check. Retries support learning; matching a number does not certify independent proficiency.
Take the investigation further
Choose any extension. These are project prompts for you to carry out; they are not automatically assessed.
School investigation
Create a new case with different numbers and explain your decision to a classmate.
College investigation
Implement or analyze a fresh case, document assumptions and compare at least two alternatives.
Workplace investigation
Prepare a decision artifact with evidence, operating constraints, an owner and a follow-up measurement.
Keep the evidence, choose your next step
Completion records your own decision that you have worked through this investigation. Practice checks and independent project evidence are separate.