What we learned replacing a spreadsheet that ran a company
It had forty tabs, one owner and no backups. It was also the most accurate model of the business anyone had.
Spreadsheets that grow into systems are not a failure of discipline. They are evidence that the business needed something the available software did not provide — and that one person cared enough to build it.
Respect the spreadsheet
Before replacing it, we documented every formula as a business rule. About a fifth were obsolete. The rest were the specification nobody had written.
Keep the owner
The person who built it understands the business better than anyone. Make them the product owner of the replacement, not the casualty of it.
The spreadsheet was never the problem. Its fragility was.
Replace in slices
We moved one tab at a time into the new system, keeping the spreadsheet as a read-only mirror until the last one. Trust transferred gradually, which is the only way trust transfers.