Update explanations

README.md

@@ -68,6 +68,27 @@ BNetzA replaces the file in place across editions, so the URL is
 stable; the fetcher detects updates via the HTTP `Last-Modified`
 header.
 
+## Exam aids (Hilfsmittel)
+
+BNetzA publishes an official aid sheet that candidates **are allowed to
+use during the exam** — you do not have to memorize anything it
+contains:
+
+- [`Hilfsmittel_12062024.pdf`](https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/AntraegeFormulare/Hilfsmittel_12062024.pdf?__blob=publicationFile&v=3)
+
+It bundles the BNetzA frequency-allocation table (band limits, usage
+parameters, and maximum power per class), the IARU band plans, the
+German *Rufzeichenplan* (call-sign series → class plus the
+international suffixes like `/m`, `/mm`, `/p`), and the *Formelsammlung*
+(formula collection) together with constants and material tables. It
+does **not** contain foreign-country prefixes (*Landeskenner*),
+Q-codes, or the phonetic alphabet — those remain memory items.
+
+Questions whose answer can be read or derived from this sheet carry a
+**Hilfsmittel** note in their explanation (see below), so you can tell
+when something is a lookup in the exam rather than something to learn
+by heart.
+
 ## See also
 
 - [**50ohm.de**](https://50ohm.de/) — community-maintained
@@ -109,6 +130,13 @@ on this: questions without an entry just show no explanation block.
 Entries with `confidence < 7` render a small "low confidence" badge
 so learners know the reasoning is provisional.
 
+Where a question's answer is available in the official exam aid sheet
+(see [Exam aids (Hilfsmittel)](#exam-aids-hilfsmittel)), the explanation
+appends a short **Hilfsmittel** note — for example pointing at the
+frequency-allocation table, the IARU band plan, the Rufzeichenplan, or
+the Formelsammlung — to flag that it is a lookup you may consult during
+the exam rather than a memory item.
+
 `EXPLANATIONS.md` is the editorial contract: schema, sourcing
 guidance, confidence scale, and the workflows an AI agent should
 follow when asked to add or improve entries.