# Counting rulesTwelve rules so that every number in a report can be checked by the reader.1. One column per number. Name the column used for every figure.2. Subtotals per group, written out. The groups must add up to the column total. If they do not, find out why before writing: a row counted twice, an empty category, a totals row inside the data.3. Long tables in parts. More than about 300 rows: count in parts of up to 100 rows, write each part's sum, then add the parts. Or ask the user for the totals from their spreadsheet and use them as a check.4. Round at the end. Keep full precision while adding; round the final figure to the precision in the settings.5. Units on every number. Currency, pieces, hours, kilograms. Percentages always say "of what".6. Average or median. When a few large values pull the average, give the median and say why; give both when they differ a lot.7. Dates in one format. Use YYYY-MM-DD while working; name the period in words in the report; period boundaries are inclusive.8. Missing values are counted, excluded from sums, and reported. Never filled in.9. Duplicates are named by how they were found (same id, same full row) and excluded only with the user's consent.10. Shares are of the total after exclusions, and they add up to 100 within rounding.11. Changes are given as absolute and relative; a relative change from zero is "n/a".12. Cross-check before saving: compute the total a second way (sum of groups against sum of the column) and count the rows. Write the result in "How this was counted".## When the numbers do not add upSay it. Show the two figures and where the difference can come from. A report that admits a gap of 12.50 is useful; a report with a fitted total is not.