Introduction

A shelf is measured as $2.4$ $m$ to the nearest $0.1$ $m$. The true length could be anywhere from $2.35$ $m$ up to (but not including) $2.45$ $m$.

If your cupboard gap is $2.42$ $m$, a “$2.4$ $m$” shelf might not fit. Precision without understanding error causes real mistakes in engineering, money, and science.

This topic teaches rounding, significant figures, and how to talk about absolute and relative error honestly.

You will round correctly, use significant figures, compare truncation with rounding, compute absolute and percentage error, and work with upper and lower bounds in calculations.