A mid-program calculation milestone of our GB300-class electrical design ran ten capacity cases, 364 same-event UPS load rows, 24 one-generator-unavailable tie screenings, 160 phase-island constraints and 32 node conservation checks [STUDY], and landed its results as annotation changes to exactly two drawings — operating-duty and generator-operating-sequence sheets E-204 and E-205. The other 105 candidate drawings, and all 107 frozen source files behind them, finished the milestone hash-verified unchanged [DESIGN]. The small change count is not the finding. The finding is that the milestone could prove it.
The contract came first
Before anything ran, the milestone wrote its own rules: a scope (calculations, named supplier and protection interfaces, native annotations on an isolated copy of the prior milestone's sheets), a do-not-touch list (the two prior milestones' sources, the published Public Edition, and every other active model), a preserve list (component and wire topology and handles, the 13 UPS paths, the 16-generator four-section three-tie plant, the 30-CDU dual-input mapping), acceptance criteria, stop conditions, and a hard limit of two remediation cycles. One rule does disproportionate work: unknown actual inputs stay null or explicitly symbolic — no invented OEM terminal, rating or approved load may appear anywhere in the calculation set [DESIGN]. A capacity table with honest nulls in it is a to-do list; the same table with plausible invented values is a liability.
What the calculations were allowed to touch
The run wrote its results into the two sheets through native table and text objects only: E-204's object count moved from 13 to 15 with two new tables, E-205's stayed at 9, and no circuit or device topology changed. The modified drawings were saved, reopened and read back, with component and wire identities confirmed unchanged, and a final layout pass was bounded in writing to a 2.5 percent plot-window margin adjustment and installed-versus-design wording — a scope narrow enough that reviewing it takes minutes [DESIGN]. Everything else produced by the milestone — the 24 supplier minimum-return items, the 19 functional states, the event tables — stayed in the calculation record, waiting for vendor data rather than leaking onto sheets as if confirmed.
The preservation proof
The do-not-touch list only matters if its observance is checkable. Here the milestone froze the hashes of 107 source files before starting and verified them after finishing: zero changed. The two modified drawings were themselves isolated copies, so the prior milestone's set survives intact next to its successor, and the published Public Edition was untouched by construction of the record rather than by assurance [DESIGN]. "We were careful" is a sentence; a before-and-after hash table is an artifact. Only one of them survives an audit, a handover, or a dispute two years later.
One admitted gap
The milestone's closeout also records what did not finish: the calculation workbook passed its content checks, but the native spreadsheet-to-PDF export timed out and was stopped, so the rendered-review step for the workbook is logged as incomplete and the workbook is classed for internal engineering use only [STUDY]. Writing the gap down cost one line. The alternatives — retrying until something silently passed, or shipping the workbook as if reviewed — both cost more, later, and are both invisible until they are expensive.
Limits and open items
No vendor data entered the milestone: the 24 supplier minimum-return items remain open, and every capacity conclusion is a screening on declared comparison points, not an acceptance [HOLD]. The milestone explicitly made no external release and authorized no procurement or construction step. The workbook's rendered review remains outstanding [HOLD].
Closing observation
Change control is usually argued about at the moment of change, and audited at the moment of dispute — months apart, with memory as the only bridge. A run contract written before the work, a do-not-touch list with frozen hashes, a bounded layout pass and an admitted incomplete step close that gap to zero: the milestone carries its own audit. The test worth applying to any design increment is the one this record passes — can it name every file it left alone, and prove it?
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Source: K&K Data Service Inc., "A Calculation Milestone Changed 2 Drawings of 107, and Proved It," https://www.kkdatasvc.com/lab/rfq-vendor-review-and-commissioning/a-calculation-milestone-changed-2-drawings-of-107-and-proved-it/.
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