diff --git a/counter/models.py b/counter/models.py
index 85424feb..074f761e 100644
--- a/counter/models.py
+++ b/counter/models.py
@@ -81,6 +81,11 @@ class Customer(models.Model):
         return number + letter
 
     def save(self, allow_negative=False, is_selling=False, *args, **kwargs):
+        """
+            is_selling : tell if the current action is a selling
+            allow_negative : ignored if not a selling. Allow a selling to put the account in negative
+            Those two parameters avoid blocking the save method of a customer if his account is negative
+        """
         if self.amount < 0 and (is_selling and not allow_negative):
             raise ValidationError(_("Not enough money"))
         super(Customer, self).save(*args, **kwargs)
@@ -393,6 +398,9 @@ class Selling(models.Model):
         )
 
     def save(self, allow_negative=False, *args, **kwargs):
+        """
+            allow_negative : Allow this selling to use more money than available for this user
+        """
         if not self.date:
             self.date = timezone.now()
         self.full_clean()
diff --git a/sith/settings.py b/sith/settings.py
index 81b85c10..d12d3a0b 100644
--- a/sith/settings.py
+++ b/sith/settings.py
@@ -401,6 +401,7 @@ SITH_ECOCUP_CONS = 1152
 
 SITH_ECOCUP_DECO = 1151
 
+# The limit is the maximum difference between cons and deco possible for a customer
 SITH_ECOCUP_LIMIT = 3
 
 # Defines pagination for cash summary