update

backend/README.md

@@ -39,10 +39,11 @@ uv run ruff check .
   `updataTime` types remain number for realtime and string for official.
   Redis locks prevent duplicate work across workers. Realtime region pages stay
   8 seconds apart. Failures retain the last successful data for up to 24 hours.
-- Realtime uses the arithmetic mean of displayed unit prices from rows 4–10
-  (`i.item1`, slice `[3:10]`), in 元/万金币, rounded to 2 decimals. This replaces
-  the earlier 万金币/元 average and uses a new Redis namespace so old units are
-  never returned as new prices. No BeautifulSoup or browser dependency is added.
+- Realtime selects rows 4–10 (slice `[3:10]`), converts each original unit price
+  with `1 / Price`, then averages those ratios in 万金币/元. Rounding to 2 decimals
+  happens only after averaging; prices are not rounded before conversion. A new
+  Redis namespace excludes the earlier 元/万金币 cache, whose rounded prices
+  cannot recover the original ratios. No new dependency is added.
 - Official authentication uses `HELPER_TOKEN` and `HELPER_ID`. Authentication
   failures (`returnCode=-30003`, explicit token-expiry messages or HTTP 401) can
   notify via Bark. Network errors do not trigger token-expiry notifications.