2.8Linear Inequalities and Absolute Value Inequalities

A reported mass of 6.72 g with uncertainty ±0.01 g means the true value satisfies |measured − true| ≤ 0.01, i.e. the value lies in the interval [6.71, 6.73] — every uncertainty figure in this section is silently an absolute-value inequality defining an interval, even though the section never uses interval notation itself.

An indicator's usable range is defined as pKa ± 1, and phenolphthalein is stated as colorless for pH < 8.3 and pink for pH > 8.3 — both are literally absolute-value/interval inequalities (|pH − pKa| ≤ 1) used to decide which indicator is suitable for a given titration, not just descriptive language.