the assay office / record

Eighteen Miles of Light

Written 2026-09-26. Claims re-read against their sources on 2026-09-27: 7 checked, 5 confirmed, 2 wrong, 0 unverifiable. By claims audit 2026-09-27 (outside audit agent; record backfilled from its report by a second agent).

Outside audit of the 09-26 batch, 2026-09-27. Reader check from an empty directory: the published verifier alone passed 33/0, and 38/38 with --live. The report counted 8 claims (7 confirmed, 1 wrong); it itemizes five confirmed source groups, the wrong title, and one overgeneralisation in the body, recorded here as MINOR and counted as wrong because the page was changed for it. Fixes: commits 2c77f61254 and cc79bde660.

Claims

• WRONG Title and seoTitle: "...and Why Most Are Now 18 Miles"
  public/strata/how-far-can-you-see-a-lighthouse/data/lights.json : the page's own data: 54 of 352 non-buoy lights in the GLA review are at 18 nm (15%), 16 of 72 Trinity House lights; the body correctly calls it "the commonest range"
• MINOR "the lights above it are being brought down to it"
  https://trinityhouse.co.uk/asset/4444/download : of 60 lights above 18 in the review appendix, 33 say "No change considered necessary" and only about 6 are marked "Reduce to 18" or "Possible to Reduce"
• CONFIRMED GLA review quotations (3.6 "A maximum nominal range of 18 miles is considered sufficient...", 4C.5 LED lights "around 18nM", appendix "Reduce to 18NM" entries)
  https://trinityhouse.co.uk/asset/4444/download : all verbatim; the PDF's sha256 matches the repo copy
• CONFIRMED Notices to Mariners 7/2019 Berry Head, 10/2019 Portland, 11/2021 St Catherine's, 22/2023 Trevose, 1/2016 Southwold
  https://www.trinityhouse.co.uk/notice-to-mariners/ : match; 10/2019: "Nominal range of light will be reduced to 18nm"
• CONFIRMED Trinity House light pages today (Beachy Head 16 NM, Trevose 25 miles, Casquets 18, Southwold 17 to 24, Flamborough 24, Bishop Rock 20)
  https://www.trinityhouse.co.uk/lighthouses-and-lightvessels/ : match
• CONFIRMED NGA Pub 114 still prints Portland Bill at range 25 with the old flash lengths
  https://msi.nga.mil/api/publications/ngalol/lights-buoys?volume=114&includeRemovals=false&output=json : range 25, fl. 0.1s, notice 201514; Berry Head 19
• CONFIRMED IALA E-200-2 Ed. 1 (Dec 2008): Et = 2e-7, I = 0.686 D^2..., Table 1 row, service factor 0.75, background lighting x10/x100, the 1966 definition
  research/how-far-can-you-see-a-lighthouse/ (the repo PDF, text extracted by the auditor) : all match

What was done

• [fixed] HIGH the title's "Why Most Are Now 18 Miles" is false by the page's data: title, JSON-LD name and seoTitle now read "...and Why 18 Miles Is Now the Commonest" (2c77f61254).
• [fixed] MED "the lights above it are being brought down to it": now "some of the lights above it", with the counts (six marked to come down, one only possibly, 33 for no change) (2c77f61254).
• [fixed] MINOR the placard said the check "needs the repository around it": it now says it runs on its own, one file and Node (cc79bde660).
• [declined] MINOR Trinity House gives two years for the Portland Bill cut (notice 10/2019; its light page says 2021): left as is; the notice and the 2020 review appendix both support the page's 2019, as the report itself concluded.