diff --git a/esbo_etc/classes/IRadiant.py b/esbo_etc/classes/IRadiant.py
index 756ad4d..977ee5a 100644
--- a/esbo_etc/classes/IRadiant.py
+++ b/esbo_etc/classes/IRadiant.py
@@ -20,7 +20,7 @@ class IRadiant(ABC):
         size : str
             The size of the target.
         obstruction : float
-            The obstruction factor.
+            The obstruction factor as A_ob / A_ap.
         """
         pass
 
diff --git a/esbo_etc/classes/optical_component/AOpticalComponent.py b/esbo_etc/classes/optical_component/AOpticalComponent.py
index 222a90f..6f15bc9 100644
--- a/esbo_etc/classes/optical_component/AOpticalComponent.py
+++ b/esbo_etc/classes/optical_component/AOpticalComponent.py
@@ -63,7 +63,7 @@ class AOpticalComponent(IRadiant):
         size : str
             The size of the target.
         obstruction : float
-            The obstruction factor.
+            The obstruction factor as A_ob / A_ap.
         """
         signal, size, obstruction = self.__parent.calcSignal()
         info("Calculating signal for class '" + self.__class__.__name__ + "'.")
diff --git a/esbo_etc/classes/target/ATarget.py b/esbo_etc/classes/target/ATarget.py
index fd1c3cf..380c740 100644
--- a/esbo_etc/classes/target/ATarget.py
+++ b/esbo_etc/classes/target/ATarget.py
@@ -57,7 +57,7 @@ class ATarget(IRadiant):
         size : str
             The size of the target.
         obstruction : float
-            The obstruction factor.
+            The obstruction factor as A_ob / A_ap.
         """
         info("Calculating Signal for class '" + self.__class__.__name__ + "'.")
         debug(self.__sfd)