Make the expression explicit
Use parentheses and state what is included. A 20% reserve applied to an initial budget differs from a 20% share of the final total. Retain the expression in your worksheet so another person can reproduce the calculation.
Align the units
Identify every input: hours, days, euros excluding taxes, quantities or percentages. Before converting, verify the starting and destination units. For currency, specify the date and chosen rate; a mathematical conversion is not an executable commercial quotation.
Test simple values
Repeat the calculation with zero, one unit and an example easy to calculate mentally. A growth rate with a zero baseline should be identified as undefined. Keep extra precision in intermediate operations and explain how the displayed result is rounded.
Show a verifiable answer
Display the result, unit, parameters and limitations together. Google Search documentation explains its calculator and converter; our local tools also let you inspect a budget or campaign economics. A screenshot of the final number alone cannot explain the scenario or reproduce the operation.
- Write the formula
- Align units
- Test boundaries
- Show context
Worked example
Fictional example: 10 hours × €100 produces €1,000. A 20% reserve on this amount adds €200, giving €1,200. If the reserve must represent 20% of the final total, the expression is €1,000 ÷ 0.8 = €1,250. The same percentage describes two different bases.
Check before moving on
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Sources & method
Sources reviewed on 1 October 2026. Worked calculations use explicitly hypothetical inputs.
Topic provenance: Pas de calculatrice ? Google Calculator (2008-02-11). Search Engine Feng Shui. Byline retained in the consulted version: Thomas Poulard.
This guide is newly written in 2026. It does not reproduce the earlier text and is not attributed to its historical author.