# ATGMS (Automated Track Geometry Measurement System) revision history

Append-only Arc G field-change log. Forward-only honesty: events accrue from Arc G adoption.

Model: [ATGMS (Automated Track Geometry Measurement System)](/models/ns-atgms.md)

_No events on file. Arc G is forward-only; the recorded event log accrues from Arc G adoption (2026-06-04) and records material changes as they flow through the updateEntityField chokepoint. For the current state of this model, see the model page._

## Forward-only note

Arc G is forward-only. The event log accrues from the Arc G adoption point. Fields with no events post-baseline equal the current cached value and are not independently verified at any prior date. To restate a recorded change, write a new event through the updateEntityField chokepoint.

_Canonical URL: /models/ns-atgms/history. REST: /v1/models/5eefc909-a672-4174-9840-9e355f110f27/history. HTML: [/models/ns-atgms/history](/models/ns-atgms/history)._