Wanted outcome: a measurement rule someone else can follow. Prepare: O5; optional ruler and two pre-made ordinary paper stems. Complete supplied alternative: stem S measured soil-line-to-tip 28 mm; container-base-to-tip 43 mm; reference-point difference 15 mm. These are constructed model values.
0–3: Two “height” readings differ; ask whether either must be dishonest. 3–9 model: show the different reference points. Model soil line to tip, ruler zero at the line, eye level, nearest mm where the ruler allows it. 43 − 28 = 15 mm comes from reference choice, not growth. 9–21: choose a route. 21–27: compare methods, not people; mark what was measured versus supplied. 27–30 exit: state a reference point and unit. If precision is vague, choose a ruler scale and a consistent reading rule.
- Route 3A · Paper measuring job. On ordinary paper draw a stem with a base line and tip; select and use a millimetre ruler to measure it three times without changing the drawing. Record all actual readings, reference, scale and any difference. No prescribed “correct” invented result; ask whether ruler placement varied. Without equipment, use the supplied 28/43 mm pair and mark supplied, not personally measured.
- Route 3B · Method comparison. Make a side-by-side rule for River and Ridge from O5. Explain why their numbers are not directly comparable and propose a common soil-line-to-tip rule, same stage/time, ruler scale and eye level. All resulting outcomes remain not observed.
- Route 3C · Precision dilemma. A fictional rounded record says “about 3 cm” for two stems; a finer record says 28 mm and 32 mm. Convert 3 cm to 30 mm, then explain how rounding can hide a 4 mm difference. Choose a precision appropriate to the question; do not claim more accuracy than the instrument or method supports.