Four questions that determine which tier a simulator belongs to
No methodology jargon. No standards language. This page explains classification the way you would explain it to someone who has never encountered the framework before, using plain descriptions of what is actually being asked at each step.
Every classification question, every piece of evidence, every criterion in the formal methodology is ultimately working toward a single determination:
All four questions below refine this core question. The first asks about the source of the motion. The second asks about the delivery path. The third asks about what actually arrives. The fourth asks how we know. Together they narrow down to one of three classification results.
A simulator has a physics engine — software that calculates what the vehicle is doing at every moment: how much it is turning, braking, accelerating, rolling, pitching. Question 1 asks: does the platform's motion come directly from those calculations, or does it come from somewhere else?
Physics-derived (passes Question 1):
Effect-layer (fails Question 1):
Even if motion originates from the physics engine, it has to travel to the participant through the mechanical structure of the platform. Question 2 asks whether that delivery preserves the physics-derived signal correctly — or whether the mechanical architecture distorts it.
Two things matter here: whether each axis of motion (forward/back, left/right, up/down, and three rotational directions) operates independently, and whether the rotational calculations are referenced to the vehicle's center of mass.
The hexapod is a common platform configuration. It achieves six degrees of freedom through six actuator legs — but all six DOF are resolved simultaneously through the kinematics of those six legs. There is no independent axis. A command to produce yaw rotation requires coordinated changes across all six legs. This is mechanically inherent to the hexapod geometry and cannot be designed around without changing the fundamental configuration.
Questions 1 and 2 examine the architecture. Question 3 examines the result. Even if a system passes Questions 1 and 2 on paper, the actual motion characteristics — timing, magnitude, onset pattern — need to be consistent with what the inner ear would expect to detect for the vehicle events being simulated.
This is not about comfort or preference. The inner ear has specific detection characteristics: it responds to acceleration onset above a threshold, it detects direction and magnitude, and it relates timing to visual input to assess whether what it feels matches what it sees. If the motion timing or magnitude are too far outside the expected range for the depicted vehicle events, the brain receives a mismatched signal even if the architecture is correct.
A classification is only as reliable as the evidence behind it. Question 4 asks: how was each of the first three questions actually answered? Was it from directly measured data, from verified technical documentation, from manufacturer-provided specifications, or from claims in a product brochure?
These are not equally reliable. The framework assigns four evidence tiers to distinguish them. The classification result does not change based on the evidence tier — a Pass is a Pass regardless of tier — but the confidence in the result does.
A classification based entirely on Tier 1 and Tier 2 evidence is definitive. A classification based on Tier 3 or Tier 4 evidence carries uncertainty — the architecture described may differ from the architecture as implemented.
The four questions produce one of three classification results. The result depends on which combination of answers was obtained.
Motion is directly physics-derived, delivered through independent axes from a center-of-mass reference, with timing and magnitude characteristics consistent with the depicted vehicle events.
Motion is present and physically delivered to the participant, but it is not causatively derived from the vehicle physics state at time of generation. The inner ear receives motion information that does not directly correspond to what the vehicle is doing.
No physics-derived motion reaches the participant at all. The simulation is entirely visual and auditory. The inner ear receives no motion signal during the simulation event.
Classification is sometimes confused with other kinds of quality assessment. These are the most common misreadings.