Process and analysis
What is Admiralty Code?
A two character source grading scheme: a letter for how reliable the source is, a number for how credible this particular claim is.
The Admiralty Code, also called the NATO or Admiralty grading system, rates a piece of information on two separate scales. A letter from A to F says how reliable the source has been over time. A number from 1 to 6 says how credible this particular claim is, judged on its own.
Keeping the two apart is the point. A trusted source can pass on a rumour, and an unknown source can report something that other evidence confirms. A rating such as B2 tells the reader both things at once: usually reliable source, probably true claim.