ypoissant wrote:On page 214, I don't understand the sentence "When working with these error intervals, it’s important to remember that because

(1 ± em) terms represent intervals, canceling them incorrect:"

Seems fine to me. Although the numerator and denominator contain the same 'term', they don't cancel because the terms are actually intervals: (1 ± em) is the interval [(1 - em),(1 + em)], so (1 ± em)/(1 ± em) = [(1 - em)/(1 + em), (1 + em)/(1 - em)] (with 0 < em < 1).