Arc Skills / Configuration and change control

Compare two engineering baselines

Use Arc Skills to compare two captured engineering baselines and explain the material differences. Get a record diff with before-and-after values, configuration changes, evidence consequences and a clear boundary between deletion and a narrower export.

Use this skill

Use Arc Skills to compare these engineering baselines.

Inputs:
- Both exact snapshots and scope manifests
- Stable IDs, revisions and controlled document versions
- Requirement, interface, budget and evidence links

Return added, removed, changed and scope-excluded records with old/new values. Explain candidate impacts and evidence applicability. Preserve unchanged records in the count reconciliation; do not compare by names alone.

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What you provide and what you get

Inputs and outputs
What you have	How it is used	What you get
Two snapshots and scope manifests	Align stable IDs and covered areas	A reproducible baseline comparison
Controlled fields and revisions	Identify exact deltas	Added, removed, changed and unchanged counts
Evidence identity and configuration	Explain support for the later baseline	Follow-up actions by affected aspect

A renamed system is not a new system

Illustrative engineering example.

Baseline A covers the controller and ground trainer. Baseline B covers only the controller. Names change, but stable IDs identify the same engineering records.

A: SYS-1 name “Controller”; REQ-8 rev A interval ≤5 s; ICD-2 rev C; TRAIN-1 included.
B: SYS-1 name “Flight controller”; REQ-8 rev B interval ≤2 s; ICD-2 rev C; REQ-9 added.
B scope manifest explicitly excludes TRAIN-1. B retains RUN-8, executed against REQ-8 rev A.

A renamed system is not a new system
Record	Baseline A	Baseline B	Difference	Engineering consequence
SYS-1	Controller	Flight controller	Name changed; same ID	No functional change established by this field
REQ-8	Rev A: ≤5 s	Rev B: ≤2 s	Technical limit tightened	Review design capacity and TEST-8 acceptance
ICD-2	Rev C	Rev C	Unchanged captured document	Do not substitute a live latest document into either snapshot
REQ-9	Absent	Rev A present	Added obligation	Trace allocation and planned verification
TRAIN-1	Present in scope	Excluded by manifest	Scope difference	Do not report as a product deletion
RUN-8	Tests REQ-8 rev A	Same retained report	File unchanged; applicability changed	The old limit alone cannot substantiate the tighter obligation

There are six identities in the comparison: two field changes, one added record, two unchanged records and one scope exclusion. The unchanged report still has a new applicability question; a file diff and an engineering impact register answer different questions.

If B’s scope manifest were missing, TRAIN-1 would be unresolved rather than confidently excluded or deleted. The comparison preserves that distinction so the reviewer can find the required evidence.

Align identity, then explain changed meaning

Compare scope manifests before interpreting absence as deletion.
Align stable IDs and exact versions, then show old and new values.
Distinguish editorial fields from changed engineering obligations and configurations.
Assess linked evidence separately from record equality; give each material difference an owner decision.

Questions about this task

Can two records with the same name be treated as the same item?

Only if identity or an explicit migration map establishes that relationship. Names are display fields and can change or repeat.

Sources and further reading

NASA Systems Engineering Handbook: configuration management: Background on identifying configurations and controlling baseline changes.

References inspected on 3 October 2026. The worked output is an authored example using the stated inputs.