EventGauge: When Can 3D Evaluation Validate Metric Scale?

Learned 3D reconstruction increasingly claims metric depth and absolute scene scale, yet standard evaluation can remain unchanged when the recovered global scale is wrong. Similarity alignment can absorb global scale, while co-centred rendering can preserve projections under joint rescaling, removing scale evidence from both common reporting channels. We introduce EventGauge, a physical audit that withholds a calibrated displaced camera until reconstruction is frozen. The audit asks whether the finished reconstruction is best supported at the true physical viewpoint and whether that support is sharp enough to justify a metric conclusion. Controlled rescaling verifies that the response moves with scale as predicted by geometry. Across positive and failure cases, the audit can support physical consistency, expose a residual inconsistency, or remain unresolved when the evidence is too broad. EventGauge therefore turns a metric-scale claim from something standard reporting can silently absorb into a falsifiable physical test. Selecting a scale is a property of reconstruction; validating that scale is a property of evaluation.