diff --git a/docs/ecolyo/functionalities/challenge.md b/docs/ecolyo/functionalities/challenge.md
index b3037fcc260171cdb3bd9334522421e7826ed028..390e1027e8c8530a752026e5838bbc5aabd47617 100644
--- a/docs/ecolyo/functionalities/challenge.md
+++ b/docs/ecolyo/functionalities/challenge.md
@@ -50,7 +50,7 @@ Calculation of custom question is done by combination of all parameters:
 
 - If _period_ is empty.
 
-  Retrieve the **date** of day/month/year (define by _timeStep_) from the last week, month, year (define by _interval_).
+  Retrieve the **date** of day/month/year (define by _timeStep_) from the last week, month, year (define by _interval_), if there are not data in this interval, then it will go back to a previous interval, up to a maximum of 6 months
 
 ```
 example: What day did I consumme the most on the last week ?