How every workbook is tested

A spreadsheet is a small machine. A machine that looks correct while calculating wrongly is worse than no machine at all — so before any WorkbookBarn file is listed, it is tested the way an auditor would test it.

1. Build from a written spec

Every workbook starts as a specification: the tabs, the inputs, the formulas, the seed figures. The file is generated from that spec, then opened in a calculation engine and fully rebuilt so every formula actually executes.

2. Recompute independently

The headline figures are worked out a second time in code, from the same seed inputs — never read back from the sheet. That second set of numbers is written to a ledger with a tolerance for each row.

3. Compare, cell by cell

The rebuilt workbook is compared to the ledger. Every formula cell is also scanned for errors (#DIV/0!, #REF!, #VALUE!). One disagreement stops the release. Each product page shows an excerpt of its own ledger, with the sheet, the cell and the figure.

4. The free calculator is generated from the same file

The browser calculators on this site are produced from the same spec as the workbook, so the two cannot drift apart. Use the calculator first; if it earns its place, keep the workbook.

What testing does not do

Testing proves the arithmetic is right. It cannot know whether your inputs are right, or whether a figure means what you hope it means for your situation. That part is yours — and, where money is involved, your professional’s.