Valeo · security governance / February 2026
When Excel stops being a spreadsheet and becomes a critical system
The governance workbook accumulated enough logic, dependencies and manual operation that it had to be treated like a system: with versions, rules and failure modes.
Situation
By February, one central workbook was doing far more than storing data. Formulas, statuses, references, macros and manual updates from several teams depended on one another. The risk was not that the tool was Excel; it was that an informal application had emerged without the controls normally expected around software.
Approach
I first mapped which parts represented real business logic and which were only presentation conveniences. Manual copy steps and hidden dependencies were listed separately, while critical calculations were broken down into verifiable inputs. The goal was not an immediate platform rewrite, but removal of invisible rules and single-person knowledge.
Outcome
The workbook became easier to manage, and more importantly we could distinguish genuine operational risk from ordinary spreadsheet complexity. Later automation reused the underlying rules instead of cloning cell layout, which made reports easier to regenerate and failures easier to trace.