Read the unit label
MB differs from MiB and a US gallon differs from a UK gallon. Temperature readings need scale offsets, while area conversions square a length factor. Confirm the dimension and system before copying a number into another application.
Choose a date-counting rule
Elapsed date difference returns zero for the same date. Business-day counting includes both endpoints and only excludes holidays you enter. For time zones, supply a known instant with seconds and an offset; do not guess a repeated local time during a clock change.
Check precision and interpretation
Fractions and integer ratios use exact integer arithmetic; decimal calculations can round. A percent change is not a percentage-point difference, and a sample statistic does not establish significance. These are general-purpose helpers, not professional advice or official deadline determinations.