diff --git a/README.md b/README.md
index 5aa7df3..6a640cf 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,6 @@
+<!-- Footprint pad geometry in the catalog is fetched from EasyEDA/LCSC per LCSC code
+     (packageDetail.dataStr PAD records, 1 unit = 10 mil = 0.254 mm) — not derived from
+     package names. See the catalog_pads_merge function. -->
 # parts-store
 
 PromptPCB Parts — open curated component store (catalog, PBR 3D viewer, submit-with-LLM)
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