01 / Question
Name what you want to understand.
Write the choice or relationship the comparison should make clearer. Avoid starting with a chart type before the question is settled.
List what the comparison needs to include and which related matters are outside its scope.
02 / Unit
Define what one mark stands for.
Name the unit and the way the total is formed. Check that the same unit is used across the views you want to compare.
If a definition changes, explain it before treating the views as equivalent. A consistent appearance cannot repair a different underlying meaning.
03 / Whole
Keep the denominator close to the part.
Show the total beside the share or count. Use a small visual that lets a reader see how the pieces make up the whole.
Compare the absolute count with the fraction when both are relevant. Ask whether the same share could belong to a different-sized total.
04 / Read
Explain the difference without overstating it.
Write what changes, what remains constant and what the comparison does not establish. Return to the original question and check that the visual actually helps answer it.
Keep a note of any context that could change the interpretation. A clear limitation makes the comparison more useful to the next reader.