How a percentage becomes defensible
Every number EarnedCurve reports is the output of an arithmetic you can follow by hand: a set of weighted steps, a claim against each, a roll-up that conserves what it sums, and a period boundary that can't be rewritten afterwards. This page is that arithmetic, in order.
A step is done or it isn't
A rules-of-credit template is a list of production steps with weights that sum to 100. An item's percentage is the sum of the weights of the steps that have actually been completed — nothing more. There is no judgement term, no “about 60%”, and no place to put one.
| Production step | Weight | Claim basis | Claimed |
|---|---|---|---|
| Started | 5 | manual | 5 |
| Draft complete | 25 | manual | 25 |
| Issued for review (IFR) | 20 | auto — EDMS transmittal | 20 |
| Inter-discipline check (IDC) | 20 | auto — EDMS transmittal | — |
| Comments incorporated | 15 | manual | — |
| Issued for construction (IFC) | 15 | auto — EDMS transmittal | — |
| PID-2140 Rev C | 100 | — | 50% |
What goes in must come out
Every item carries a dual-basis budget: hours and value, together. The roll-up from item to activity to project conserves both — that is an engine invariant covered by tests, not a convention someone maintains by hand. A roll-up that silently loses a few hundred hours somewhere in the tree is the failure mode this design exists to make impossible.
| Item | Budget h | Budget £ | % | Earned h | Earned £ |
|---|---|---|---|---|---|
| PID-2140 Rev C | 640 | 64,000 | 50% | 320 | 32,000 |
| ISO-4471-A | 120 | 12,000 | 100% | 120 | 12,000 |
| MTO-P-0092 | 210 | 21,000 | 26% | 54.6 | 5,460 |
| → EN-PIP-1200 (L3 activity) | 970 | 97,000 | 51.0% | 494.6 | 49,460 |
The activity percentage is earned ÷ budget on the hours basis (494.6 ÷ 970). The value basis rolls up alongside it and must reconcile — if the two ever disagree, the roll-up is wrong, and the engine says so.
Step bands map Level 4 onto Level 3
A Level 3 activity in P6 is a coarser thing than the register beneath it. The bridge is a step-band map, set once per template: each band is the range of L4 steps that corresponds to a stage of the L3 activity. Once mapped, the L3 percentage derives itself — it is never typed, and it never needs to be re-agreed.
| L3 band | L4 steps it covers | Cumulative | Reads as |
|---|---|---|---|
| Band 1 — mobilised | Started | 5% | work has begun |
| Band 2 — drafting | Draft complete | 30% | deliverable exists |
| Band 3 — in review | IFR | 50% | out for comment |
| Band 4 — checked | IDC · comments incorporated | 85% | technically agreed |
| Band 5 — issued | IFC | 100% | constructible |
History is immutable; the difference is computed
Closing a period takes a snapshot. From that moment the period is history: changes land in the open period only. Every curve, histogram and skyline reads off snapshots, which is why two people opening the same report on different days see the same numbers.
What EarnedCurve is, for EVMS purposes
EarnedCurve is the performance-measurement layer of an EIA-748 EVMS — the objective earned-value truth, the time-phased plan, the variance and forecast analysis, and baseline control. It is deliberately not a cost-accounting or scheduling engine: your ERP owns actual costs and indirects, P6 owns schedule logic and dates. A compliant EVMS is the combination, and a vendor claiming otherwise is selling you two systems in one box.
| # | Guideline (EIA-748-D) | Status | Where it lives |
|---|---|---|---|
| 1 | Define work scope (WBS) | partial | Register items (L4) under activities (L3); no formal WBS builder. |
| 2 | Define project organization (OBS) | partial | Control account + CAM axis on items; reports slice by both. |
| 3 | Integrate processes | partial | Schedule, progress and mapping share activity keys; cost accumulation is external. |
| 4 | Identify overhead management | out of scope | Accounting / ERP function, by design. |
| 5 | Create control accounts (WBS × OBS) | partial | Items carry a control account and CAM; roll up with hours and value conserved. |
| 6 | Schedule the work | partial | Reads and reconciles P6; a date-drift watchdog flags slippage. P6 owns logic. |
| 7 | Objective products & milestones | supported | Core. Rules of credit = weighted objective steps. |
| 8 | Performance Measurement Baseline | supported | Baseline curve → BCWS, per period and per activity. |
| 9 | Budget by cost elements | partial | Dual-basis budget and archetypes; not a full labour / material / subcontract split. |
| 10 | Discrete work + objective measures | supported | Register items are work packages with measurable steps in hours and value. |
| 11 | Sum detail budgets to control account | supported | Roll-up conserves hours and value — engine invariant, covered by tests. |
| 12 | LOE planning & control | supported | LOE quarantined from deliverable % and reported separately. |
Guidelines 1–12 shown. The remaining twenty follow the same split and are tracked in the same living checklist against the NDIA IPMD EIA-748 Intent Guide.