Numerical Sanity Check

Core rule

A precise-looking number can still be dimensionally or conceptually wrong.

Write the units beside inputs and outputs. Check expected range, sign, ordering, and rough magnitude before trusting exact arithmetic. Recompute critical totals independently or with a calculator, especially after percentage, currency, binary/decimal size, time-zone, or per-million-token conversions.

For estimates, separate measured values from assumptions and show sensitivity to the biggest uncertain input. For rates, verify numerator/denominator and time window. For percentages, distinguish percentage points from percent change.

Reject impossible results early: negative file counts, probabilities above 1, cache savings larger than total input, or a converted value off by powers of 10.