diff --git a/Validity.md b/Validity.md
index 90cb4c5..b8f1566 100644
--- a/Validity.md
+++ b/Validity.md
@@ -41,6 +41,9 @@ Please be careful about the format,  there are only `+*d` (for days) and `+*h` (
 
 
 
+## If you use the absolute format for `--valid-to  "2022-04-01T08:10:33Z"`,   the cert will NOT be renewed automatically when it expires.  
+## If you want the cert to be renewed automatically, please use the relative format `--valid-to  +20d`(the cert will be renewed every 20 days).   Of course, if you don't use `--valid-to` parameter at all, the cert will be renewed every `60 days` as before.
+