Heuristic
Round for reporting, not by accident during calculation
Rounding errors can accumulate while each individual cell looks harmless.
When it fits
- Many small values or conversion steps feed a final total.
When to avoid it
- Prescribed billing, tax or regulatory rounding rules take precedence over this general computational habit.
Why it matters
Keep sufficient precision through the calculation and round deliberately at the reporting stage. Show no more precision than the inputs and decision justify. Distinguish a display choice from a change to stored values, especially when a total is assembled from many components.
An example
Three exact values of one third sum to one; three prematurely rounded values of 0.33 sum to 0.99.
Check your result
The rounding method is intentional, reproducible and appropriate to the context.
Keep this limit in mind
- Prescribed billing, tax or regulatory rounding rules take precedence over this general computational habit.
Connected ideas
Useful withSeparate repeatable measurements from correct measurements
Evidence and sources
Supports
Rounding intermediate measurements can change a final calculation, while extra displayed digits do not create extra measurement information.
Formal accounting and regulatory systems may prescribe specific rounding stages that take precedence.
Chemistry 2e, 1.5: Measurement Uncertainty, Accuracy, and Precision · Significant figures in calculations