docs: under reference_psf = "science" the metrics' stars are the reference catalog's; GBTDS gb3's first core, ring and registration (gate-sci-psf)

system/datasets.md

@@ -79,8 +79,13 @@ reference from the first six and three epochs differenced, every check
 clean: pointing 268.54 −28.54 SCA 8 (`r00340-gb1`), 515 packets, and
 pointing 266.71 −28.93 SCA 2 (`r00340-gb3`), 1,278 packets, every kept
 source above S/N 20. Three differences fall below the gate's
-`min_epochs`, so the gate sends a sample's sets unjudged, and under
-`reference_psf = "science"` only the usable fraction exists to judge.
+`min_epochs`, so the gate sends a sample's sets unjudged. Under
+`reference_psf = "science"` the core, ring and registration stars are the
+reference mosaic catalog's (rapid PR 465). On `r00340-gb3`'s sample (run
+139) the core is −0.036 to −0.048, the ring −0.038 to −0.039 and the
+registration offset at most 0.019 px, over 29 stars per epoch. The gate,
+replayed at `min_epochs`, holds every epoch on the core (bound ±0.025):
+the science half of ZOGY is mismatched there.
 
 ## OpenUniverse TDS
 

system/difference.md

@@ -73,7 +73,10 @@ absent, never zero, when it cannot be made: the registration offset
 PSF's stars, before the subpixel shift), the reference stars' width and
 its ratio to the science PSF's, the core (within 2.5 pixels) and ring
 (2.5 to 6) fractions of the difference over star flux at the 30 brightest
-isolated stars, the noise correlation, the usable fraction (finite and
+isolated stars (under `reference_psf = "science"`, which measures no
+reference PSF, the residual, ring and registration stars are the reference
+mosaic's SExtractor catalog mapped onto the science grid, the registration
+stars the residual stars' rule applied to it), the noise correlation, the usable fraction (finite and
 covered pixels), the candidates before the cap and the sources after it,
 those above S/N 20, and the share on a reference-catalog source within 3
 pixels. The database's `job_metrics` view exposes every job's metrics by