How evidence is weighted in SFR classification determinations.
The SFR framework defines four tiers of evidence used to assess simulation systems against the classification criteria. Higher-tier evidence takes precedence. This document expands the hierarchy into a standalone reference, explaining what each tier contains, why the ordering exists, and how the hierarchy applies in practice during evaluation.
Tier 1 evidence consists of calibrated, timestamped measurements of the system's actual behavior under defined test conditions. This means instrumented capture of the data paths relevant to each classification criterion: the physics model output, the motion actuator command, the motion actuator response, and the visual and audio output timing relative to the physics event. Tier 1 evidence is direct observation of what the system actually does — not what its documentation claims it does, and not what an observer perceives it to do.
Tier 1 is the only evidence tier that cannot be contradicted by higher-tier evidence, because it is the highest tier. It can only be supplemented or contextualized by additional Tier 1 evidence from different test conditions. Tier 2, Tier 3, and Tier 4 evidence are entirely superseded by directly conflicting Tier 1 data: if architecture documentation claims a property that measured telemetry contradicts, the telemetry prevails.
Tier 2 evidence consists of engineering specifications, system architecture documents, and design records that describe the system's intended behavior at the structural level. This includes physics model specifications, actuator specifications, synchronization architecture diagrams, and control system block diagrams. Tier 2 evidence is authoritative for structural properties that are determined by design — particularly center-of-mass reference, axis independence, and synchronization architecture — because these properties are set at design time and cannot be altered by software configuration alone.
Tier 2 evidence describes what the system is designed to do. It does not describe what the system actually does in a given operating state. For this reason, Tier 2 evidence about intended behavior is valid evidence of structural capability, but it can be contradicted by Tier 1 telemetry showing that the system is not operating as designed. Where Tier 1 and Tier 2 conflict, Tier 1 prevails and the discrepancy itself becomes an evaluation finding.
Tier 3 evidence consists of structured observation of the system during operation — without instrumentation. A trained evaluator observing the system's response to defined inputs, its motion onset timing, and its cross-channel synchronization can provide meaningful qualitative evidence about system behavior. Tier 3 evidence is useful for identifying obvious failures — a system that produces no motion, or motion that clearly precedes the physics event, is detectable through observation. It is insufficient for detecting borderline cases, cross-axis contamination, or timing discrepancies that fall within the perceptual threshold but outside the classification criteria.
Tier 3 evidence cannot override Tier 1 or Tier 2 evidence. A system that performs well in observation but fails on telemetry is classified according to the telemetry. A system that produces motion that an observer characterizes as "responsive" is not thereby classified as meeting Criterion A without architecture documentation or telemetry confirming the motion is causatively derived from live physics state.
Tier 4 evidence consists of unverified claims from manufacturers, operators, or third parties about the system's properties or performance. This includes marketing materials, brochures, website descriptions, press releases, sales presentations, and stated specifications that are not supported by engineering documentation or telemetry. Tier 4 evidence has no independent evidentiary weight. It cannot be used alone to produce a classification determination. It cannot override any other tier. It cannot supplement Tier 3 evidence to produce a higher evidentiary standing.
The function of Tier 4 information in an evaluation is to generate questions, not to answer them. A claim that a system is "in-the-loop" or "physics-based" or "fully synchronized" generates a requirement for Tier 2 documentation or Tier 1 telemetry that confirms or contradicts the claim. A Tier 4 claim that is not followed by Tier 1 or Tier 2 evidence remains unverified and cannot contribute to a classification determination.
The hierarchy exists because different evidence types have different relationships to what the framework is actually trying to measure. The framework is measuring structural properties — whether motion is causatively derived from live physics state, whether timing relationships are coherent, whether physical cues are sufficient to drive correct human response. These properties exist at the level of the system's architecture and its measured behavior. Evidence about those properties that is closer to the source carries more weight than evidence that is further from it.
| If Tier 1 conflicts with… | Result |
|---|---|
| Tier 2 (architecture docs) | Tier 1 prevails. The system is not operating as designed. Both the classification and the discrepancy are recorded. |
| Tier 3 (observed behavior) | Tier 1 prevails. Observer perception does not override measurement. The observer assessment is noted as a finding. |
| Tier 4 (manufacturer claims) | Tier 1 prevails. The claim is contradicted by measurement. This is itself an evaluation finding. |
| If Tier 2 conflicts with… | Result |
|---|---|
| Tier 3 (observed behavior) | Tier 2 prevails for structural properties. Observed behavior cannot override documented architecture for properties determined at design time. |
| Tier 4 (manufacturer claims) | Tier 2 prevails. Architecture documentation is a higher-quality claim than a marketing assertion about the same property. |
The hierarchy is not a preference. It reflects proximity to the property being measured. Measurement is closer to ground truth than documentation, which is closer than observation, which is closer than assertion.
In a typical evaluation, multiple evidence tiers may be present simultaneously. The evaluator applies the following process:
For the complete evaluation process, see Evaluation Process. For what evidence documents to request from a vendor before evaluation, see Procurement Guidance.
A classification determination produced from Tier 1 telemetry is a strong result — it reflects what the system actually does under defined test conditions. A determination produced from Tier 2 documentation only reflects what the system is designed to do. A determination produced from Tier 4 claims only reflects what the manufacturer says the system does. These are three very different things. The evidence hierarchy exists to make that difference explicit in every classification record.