diff --git a/notes_tools/tools/bareme.py b/notes_tools/tools/bareme.py
index c8ba831..0784689 100644
--- a/notes_tools/tools/bareme.py
+++ b/notes_tools/tools/bareme.py
@@ -37,13 +37,14 @@ def tranform_scale(eval_df, new_scale, method):
     :returns: the transformed eval_df
 
     """
+    df = eval_df.copy()
     for c in ["Bareme", "Mark", "Mark_barem"]:
         try:
-            eval_df[c+"_old"]
+            df[c+"_old"]
         except KeyError:
-            eval_df[c+"_old"] = eval_df[c]
+            df[c+"_old"] = df[c]
 
-    eval_df["Bareme"] = new_scale 
+    df["Bareme"] = new_scale 
 
     TRANFS = {"min": new_scale_min,
             "prop": new_scale_proportionnal,
@@ -51,12 +52,12 @@ def tranform_scale(eval_df, new_scale, method):
     try:
         t = TRANFS[method]
     except KeyError:
-        eval_df["Mark"] = eval_df.apply(method)
+        df["Mark"] = df.apply(method)
     else:
-        eval_df["Mark"] = eval_df.apply(t, axis=1)
+        df["Mark"] = df.apply(t, axis=1)
 
-    eval_df["Mark_barem"] = compute_mark_barem(eval_df)
-    return eval_df
+    df["Mark_barem"] = compute_mark_barem(df)
+    return df