The visible edit may be one glass note or handle code; the cost event may run through drawings, purchased material, machining, testing, packing, freight and adjacent trades. Price the causal chain, not the red cloud.
A revised elevation changes six opening marks after profiles have been cut. The request describes only the new glass and asks for a unit-rate difference. That comparison misses unusable material, engineering reissue, remanufacture, retesting, package changes and the effect on a consolidated shipment. The opposite error is equally serious: adding an unexplained lump sum and calling every delay a consequence of the change. A defensible change record preserves the last authorised baseline, isolates the affected scope, distinguishes incurred cost from forecast impact, and shows evidence for each causal step. It does not decide contractual entitlement.
1. Freeze the baseline before measuring the delta
Identify the last authorised drawing, specification, opening schedule, finish sample, hardware schedule, evidence plan, price schedule and programme. Record the proposed revision separately. If the baseline itself is disputed, label that issue rather than manufacturing a clean comparison from mixed revisions.
Build an affected-mark register. A change to one type can reach repeated opening marks, spares, samples, mock-ups, test specimens, labels, manuals and already packed units. State which items were not reviewed. The register is a scoping tool, not proof that every listed consequence is compensable.
UNCITRAL's CISG Article 29 addresses modification or termination by agreement where the Convention applies; formal requirements and party conduct can matter. It does not turn an email, drawing upload or factory action into an automatically authorised price change. Preserve the instruction, authority, timing and acceptance route for transaction-specific legal review.
| Control | Record | Question before valuation |
|---|---|---|
| Authorised baseline | Document IDs, revisions, dates and approval status | What was the supplier released to do? |
| Proposed delta | Changed requirement with originator and date | Is it a request, instruction, option or correction? |
| Affected identity | Opening marks, line IDs, lots, samples and packages | Can each consequence be mapped to real scope? |
| Status at cut-off | Designed / ordered / received / cut / assembled / glazed / packed / shipped | What work or commitment already existed? |
| Authority | Named approval route and current disposition | Who may approve technical, value and programme effects? |
| Uncertainty | Open assumptions, owner, due date and sensitivity | What cannot yet be priced as a fact? |
2. Trace the full cost tree without double counting
Start with direct quantity and specification deltas, then follow the production route. Possible effects include redesign, revised bills of material, new programming or tooling, cancellation charges, material already committed, segregation, rework, scrap, extra inspection, new samples or tests, repacking and changed transport geometry. Include an item only when the causal link, quantity, status and valuation basis are stated.
Separate four buckets: work avoided; new work; abortive or unusable work; and secondary effects. Credit genuine savings using the same transparent basis applied to additions. Keep tax, currency, freight, overhead, profit, contingency and escalation as distinct labelled components only where the authorised commercial route permits them—never hide them inside material quantities.
Record actual incurred amounts separately from supplier forecasts and buyer allowances. Purchase orders, time records and disposal evidence can support facts, but commercially sensitive records may be redacted while preserving identity, date, quantity and calculation logic. A supplier invoice proves a charge was recorded; it does not by itself establish contractual entitlement or reasonableness.
| Layer | Evidence candidates | Duplicate-risk check |
|---|---|---|
| Avoided baseline | Cancelled quantity and original authorised basis | Is the saving credited elsewhere? |
| Replacement scope | Revised quantity, controlled specification and rate basis | Does a unit-rate delta already include labour/waste? |
| Committed/abortive work | Order, receipt, production status, recovery or reuse disposition | Is full value claimed despite reuse, return or salvage? |
| Engineering/quality | Named tasks, hours, outputs, tests and revision records | Is routine baseline work being charged again? |
| Packing/logistics | Package redesign, booking amendment, storage or split-shipment evidence | Is freight included in both line and lump sum? |
| Adjustments | Expressly permitted mark-up, currency, tax or contingency basis | Is the basis authorised and arithmetically visible? |
3. Analyse time and knock-on scope as a network, not a slogan
Show the logic path from the changed input to affected engineering, procurement, production, testing, inspection, packing and shipment activities. Record remaining float or alternatives and the status date. 'Adds four weeks' without activity logic is weak; 'no delay' without checking a constrained coating slot or consolidated container is equally weak.
Distinguish the time needed to perform changed work from the effect on a contractual milestone. The latter depends on sequencing, float, concurrent events, mitigation, release timing and the signed programme provisions. Preserve alternative scenarios—expedite, partial release, split shipment or resequencing—with their costs and new risks; do not present them as obligations or guaranteed recoveries.
Map interfaces beyond the supplier: structural openings, anchors, waterproofing details, electrical access control, finishes, lifting plans, customs documents and site receiving. Each proposed consequence needs an owner and evidence. ICC's hardship and force-majeure models concern particular contractual risk mechanisms; they are not shortcuts for valuing an ordinary instructed design revision.
| Field | Minimum record | Boundary |
|---|---|---|
| Status date | Actual progress and commitments at a fixed date | Not a reconstructed hindsight baseline |
| Changed activities | Duration, logic predecessors/successors and resources | Not an unsupported calendar addition |
| Milestones | Affected date, available float and scenario | Not automatic entitlement to extension |
| Concurrent/open events | Separate event IDs and current evidence | Do not attribute all movement to one change |
| Mitigation options | Decision deadline, cost, feasibility and residual risk | Proposal, not guaranteed recovery |
| Downstream interfaces | Owner, required revision and release state | Supplier scope distinguished from third-party scope |
FAQ
Is the new-minus-old unit price the full change value?
Not necessarily. It may miss avoided work, commitments, rework, evidence, packing, freight and downstream effects—or double count items already inside the unit rate. Build and reconcile the causal cost tree.
Does drawing approval approve the variation price?
Do not assume so. Record technical, commercial and programme authorities separately under the signed process.
Can unused material be charged at full value?
That depends on the contract and facts. Record ownership, return, reuse, recovery and salvage evidence; do not decide entitlement from this guide.
Does every design change extend delivery?
No. Test the activity logic, status, float, constraints, concurrent events and alternatives. Contractual time treatment requires authorised professional review.
Should the original line be overwritten?
No. Retain it and create a linked authorised revision or disposition so quantities, value and evidence remain auditable.
Is force majeure the right label for a buyer design revision?
Not automatically. ICC's model clause has defined conditions; obtain transaction-specific legal review rather than using the label as a valuation shortcut.
Continue the project review
Connect this guide with the proposed window and door systems, then review how Cavorlen approaches manufacturing and quality control. When your schedule is ready, send it through the project review form.
Official sources used
UNCITRAL — CISG official text and explanatory material ↗UNCITRAL — Digest of Case Law on the CISG ↗ISO 10013:2021 — Guidance for documented information ↗ICC — Force Majeure and Hardship Clauses ↗Related buyer guides
This article is general procurement education, not legal, quantity-surveying, accounting, tax, insurance or contract advice. It does not interpret a variation clause, establish causation, entitlement, damages, waiver, mitigation, ownership of rejected materials or a right to time or money. It supplies no rates, mark-ups, percentages, notice periods or Cavorlen prices, policies, capacity or lead times. The signed contract, governing law, authorised designers and commercial/legal professionals control the actual change.