diff --git a/ess/lib_tw.py b/ess/lib_tw.py
index 30684a9f304295480ca437fded3fea6a53204771..e83f8ef20aa33e914e5a3be59e298ec2791abfce 100644
--- a/ess/lib_tw.py
+++ b/ess/lib_tw.py
@@ -36,9 +36,13 @@ class LATTICE:
     def __init__(self,file_name_lat,file_name_fmap=[],freq=352.21,gamma=1.0):
         '''
         :param file_name_lat: name of lattice file
-        :param file_name_fmap: list of file map files
+        :type file_name_lat: str
+        :param file_name_fmap: list of file map file(-s)
+        :type file_name_fmap: list or str
         :param freq: RF frequency
+        :type freq: float
         :param gamma: relativistic gamma
+        :type gamma: float
         '''
 
         # In case file_name_fmap is str