Boundary
Diagram reading is not measurement of an actual rock or scaled instrument operation.
Complete source
Fictional tape diagram has zero, 1, 2, 3, 4 cm marks and a paper label spanning zero to four. Five tick marks bound four intervals.
Invitation
Use large paper steps or pointing to show the measured length.
Next try
Measure a different actual paper strip with a familiar ruler if supervised and wanted; keep its own record.
Ordinary possible response
The span is 4 cm: I count the intervals from zero, not all five marks.
Title
Interval walk on paper