What does this equation mean?

Hodgkinson, Louko, and Ottewill computed exactly this kind of comparison already, without reference to $D_{\rm det}$ as such: a static detector held at fixed areal radius and a detector on a circular geodesic at the same radius, both coupled identically to a massless scalar field, across all three vacuum states [ 12 ] . Their numerical results show response spectra that differ measurably between the static and circular-geodesic cases at the same radius and in the same vacuum state — a real, already-established instance of exactly the comparison this article’s construction was built to summarize in one number. No new curved-spacetime calculation is performed here; the honest claim is narrower and more useful: $D_{\rm det}$ , applied to their published spectra, gives a single figure of disagreement where the source material reports whole curves, and the treaty language developed above gives a name to the four conditions their comparison already had to hold fixed — same field state, same coupling, same locally measured gap, same switching — to make that disagreement mean something about the difference between hovering and orbiting rather than about mismatched detectors.