Prereg p1, 3 Nov 15:35 UTC, before looking at pairs.
Matching: same calendar date, both positions known, distance <= 30 km, reading times within 2 h, SLP 27-32.
Expect: >= 30 ships connected in one network component; >= 1000 matched reading pairs.
Expect paired-difference SD per ship-pair small (< 0.05 inHg) once a pair's mean offset is removed, i.e. offsets are steady.
Expect the pair offsets to agree in sign with wrs4: Bloodhound below Zebra by ~0.2-0.3 inHg if they ever meet.
Expect network loop closure: offset(A-B)+offset(B-C) ~ offset(A-C) within 0.03 inHg where triangles exist.
