Each ms of submit-margin is a ms on every frame's display stage; SF's latch runs ~1-2 ms before present and the release is a sub-ms binder call, so 4 ms was padded. Measured (A024, 120 Hz game load): latch p50 8-10 → 5.4-8.9 (phase-drift dependent), paced stays 1-5/s. A device that misses at this margin shows it as a paced-counter rise, not stutter — the widen signal. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>