diff --git a/README.md b/README.md
index 9be0630..b1c9040 100644
--- a/README.md
+++ b/README.md
@@ -151,8 +151,6 @@ conf.probe.etherpad.database.password=
 conf.probe.target=/srv/statoolinfos/well-known/statoolinfos/foo.bar.org-metrics.properties
 ```
 
-
-
 ### Framdadate metrics (coming soon)
 
 Configuration template:
@@ -273,4 +271,6 @@ conf.probe.target=/srv/statoolinfos/well-known/statoolinfos/foo.bar.org-metrics.
 # Custom access log pattern with Java regex.
 # Default: "^(?<remoteAddress>[a-zA-F0-9\\\\:\\\\.]+) - (?<remoteUser>[^\\[]+) \\[(?<time>[^\\]]+)\\] \"(?<request>.*)\" (?<status>\\d+) (?<bodyBytesSent>\\d+) \"(?<referer>.*)\" \"(?<userAgent>[^\"]*)\".*$"
 conf.probe.httpaccesslog.pattern=
-```
\ No newline at end of file
+```
+
+Warning: to have month metric values, you have to set retention log to *7 weeks or 50 days in nginx or Apache logrotate* configuration.
\ No newline at end of file