The problem: a figure without its context
On a long-running project, the question keeps coming back: what did we promise, and on what assumptions? The offer went through five versions before signature. The hourly rate of a category was corrected two years later. The organisation changed and some positions disappeared. In a spreadsheet or a tool that only keeps the current state, each of these changes rewrites the past: the original offer can no longer be reconstructed, and a variance observed today can no longer be told apart from a correction to the reference data.
A revision is a complete snapshot
In Waterfall, everything entered on a project is entered in a revision. It contains:
- its cost structures: the main structure (schedule and estimate), and where applicable the contract amendment differentials and each risk’s own estimate;
- the reference data values they use: resource roles, calendars, cost categories and hourly rates;
- the parameters that computed or qualified it: its reference year, the inflation rate and the project’s win probability.
A revision also carries a version name and a description, in which the project manager records their assumptions. A reorganisation or a rate correction, years later, does not move it: it keeps the rates that were used to compute it.
Draft, then marked
A revision has two states. As a draft, it is where everything happens: data entry, imports, re-estimation. A project only ever has one at a time. Once marked, it is frozen and can no longer be modified by any means, whether data entry, import or automatic processing. Work then continues in the next revision, which takes over the structures of the last marked revision.
Like a tag in a version control system, a marked revision no longer moves.
A draft revision can be discarded as long as it has not been marked: the project then returns to its state at the last marked revision.
During the offer: the history of negotiations
During costing, each version submitted to the client is a marked revision. The scope removed at the buyer’s request, the subcontracting assumption dropped, the risk added after the site visit: everything remains available, version by version. Two marked revisions can be compared: tasks added, removed or modified (dates, duration, state), and differences in amounts by cost type and by sub-project.
With each new revision, Waterfall takes the current year as the reference year. When it changes, it presents, category by category, the rate kept and the reference data rate for the new year, and the project manager accepts or rejects each update. An offer therefore never changes rates without its author knowing.
Contract award: designating the baseline revision
At signature, the project manager designates, among the marked revisions, the one that is authoritative: the baseline revision. It sets the baseline budget, the risk reserve, the contractual dates and the planned value. This designation can be corrected as long as it has had no consequence, that is, as long as no actual cost has been imported and no revision has been marked since. Beyond that point, the baseline only moves when a contract amendment is signed.
During execution: one revision per review
Each periodic review produces a revision: the project manager updates the schedule and the estimate to complete, re-examines the risks, imports the actual costs, then marks the revision. The indicators of that revision are computed at its marking date and kept. This series of snapshots is what makes it possible to plot how the indices evolve review after review, or the milestone trend chart, which shows how the forecast date of each milestone slipped from one review to the next.
Tasks and lines keep their identity from one revision to the next: the lineage. It is what makes it possible to compare two revisions, follow a task over time, and re-import an Excel or MS Project file without creating duplicates.
A life cycle deduced from facts
A project goes through six states: Created, Costing, In progress, then one of the three final states, Completed, Lost or Abandoned. The first two transitions are never triggered by hand; they are deduced from facts. The project moves to Costing as soon as it has its first revision, and to In progress as soon as it has both a baseline revision and the ERP project code. A status that is moved forward by hand ends up describing the intention of whoever clicked; deduced from a fact, it stays true without anyone having to watch over it.
The only human decisions are the exits. They are confirmed, dated, optionally justified, and irreversible: a closed project becomes a read-only archive, fully viewable. Its value lies precisely in being read again, to cost the next one or to justify the previous one.