Protocol
Let the units check the formula
Units are a second line of reasoning, not decoration after the answer.
When it fits
- A calculation mixes quantities, conversions or rates.
When to avoid it
- Correct dimensions cannot detect every missing factor or incorrect assumption. Squared and cubed units require squared and cubed conversion factors.
Why it matters
Keep units attached while calculating. Cancel them algebraically and check whether the remaining unit matches the requested result. A formula that leaves hours squared when you need hours has exposed a problem before the final number can look persuasive.
Steps
- Write the input quantities with their actual units.
- Apply explicit conversion factors and cancel matching units.
- Check the output dimension and then check whether the model makes sense.
An example
Dividing 240 records by 60 records per minute leaves 4 minutes; multiplying those inputs does not produce a duration.
Check your result
Both the number and the resulting unit answer the stated question.
Keep this limit in mind
- Correct dimensions cannot detect every missing factor or incorrect assumption. Squared and cubed units require squared and cubed conversion factors.
Connected ideas
Useful withBuild an overall rate from totals
Evidence and sources
Supports
A numerical quantity requires its unit, and valid unit conversions preserve the represented physical quantity.
Matching dimensions is a necessary check, not proof that the entire physical model is correct.
SI Unit Rules and Style Conventions Checklist · Quantity values and unit notation