Method

A spreadsheet tutorial is only useful if the numbers in it are right. The check here is mechanical: the file is built, recalculated by a second engine, and every number the tutorial claims is compared against a computation written independently of the spreadsheet.

The procedure

1. Build with formulas. The workbook is built with live formulas in the cells. No result is typed in by hand. The build tool is openpyxl; the file it writes contains formulas only.
2. Recalculate in a real engine. The file is recalculated by LibreOffice in headless mode. LibreOffice is a different calculation engine from Excel and from the build tool, so a formula that only works in one place shows up here.
3. Read the values back. The recalculated file is read with openpyxl in data-only mode, which returns the computed values, not the formulas.
4. Compare against an independent computation. The expected values are computed separately in Python, from the same inputs, without using the spreadsheet formulas. A tutorial ships only when the recalculated values match the independent computation within $0.01.
5. Attach the file. The download on the tutorial page is the file that passed. The versions used and the measured results are printed on the page.

What the check does not do

The check confirms the arithmetic in the file on the versions listed. It does not test every version of Excel. It also does not check your lender's statement. A lender rounds each payment and each interest charge to the cent and adjusts the final payment, so a schedule built from unrounded formulas can differ from a bank statement by a few cents. Where a formula is version-gated, the tutorial says so on the page.

Versions used for the first tutorials

Checked 10 November 2026. Versions are recorded again on each tutorial page when they change.