diff --git a/sensospot_data/__init__.py b/sensospot_data/__init__.py
index 6a1332c..2a846d3 100644
--- a/sensospot_data/__init__.py
+++ b/sensospot_data/__init__.py
@@ -83,7 +83,7 @@ def _parse_one_folder(source, outfile, quiet):
 
 
 def _parse_recursive(source, outfile, quiet):
-    """parses all folder one level down and collects the data"""
+    """parses all folders one level down and collects the data"""
     child_outfile = DEFAULT_OUTPUT_FILENAME
     source_path = Path(source)
     folders = (i for i in source_path.iterdir() if i.is_dir())
diff --git a/sensospot_data/columns.py b/sensospot_data/columns.py
index b2f5a29..4b177aa 100644
--- a/sensospot_data/columns.py
+++ b/sensospot_data/columns.py
@@ -80,3 +80,18 @@ RAW_DATA_NUMERIC_COLUMNS = {
     RAW_DATA_BKG_SUM,
     RAW_DATA_SPOT_SUM,
 }
+
+# common indexes
+
+INDEX_COLUMNS_WELL = (
+    META_DATA_ANALYSIS_NAME,
+    META_DATA_WELL_NAME,
+    META_DATA_WELL_ROW,
+)
+
+INDEX_COLUMNS_POS = (
+    META_DATA_ANALYSIS_NAME,
+    META_DATA_WELL_NAME,
+    META_DATA_WELL_ROW,
+    RAW_DATA_POS_ID,
+)