diff --git a/tricco/prepare.py b/tricco/prepare.py
index ccd7a862014b9f84b925eec96caac191a9ecc217..2f8a1c1eb908750a851b0cb1580b0fdbab1a8305 100644
--- a/tricco/prepare.py
+++ b/tricco/prepare.py
@@ -15,13 +15,13 @@ import xarray as xr
 
 def prepare_grid(model, path, file):
     if model == 'ICON':
-        _ds_grid = __grid_icon(path+file)
+        _ds_grid = _grid_icon(path+file)
     return _ds_grid
 
 
 # implementation for ICON model
 
-def __grid_icon(_gridfile):
+def _grid_icon(_gridfile):
     
     ds_grid = xr.open_dataset(_gridfile)
     ds_grid = ds_grid[['neighbor_cell_index', 'edge_of_cell', 'edge_vertices']]
@@ -52,19 +52,19 @@ def __grid_icon(_gridfile):
 
 def prepare_field(model, path, file, var, threshold, cubulation):
     if model == 'ICON':
-        _field, _field_cube = __field_icon(path, file, var, threshold, cubulation)
+        _field, _field_cube = _field_icon(path, file, var, threshold, cubulation)
     return _field, _field_cube
 
 def prepare_field_lev(model, path, file, var, threshold, cubulation):
     if model == 'ICON':
-        _field, _field_cube = __field_icon_lev(path, file, var, threshold, cubulation)
+        _field, _field_cube = _field_icon_lev(path, file, var, threshold, cubulation)
     return _field, _field_cube
 
 
 # implementation for ICON model
 
 # single-level data
-def __field_icon(path, file, var, threshold, cubulation):
+def _field_icon(path, file, var, threshold, cubulation):
     
     # field on triangular grid
     field = xr.open_dataset(path + file)[var].squeeze().values
@@ -90,7 +90,7 @@ def __field_icon(path, file, var, threshold, cubulation):
     return field, field_cube
 
 # data on multiple levels
-def __field_icon_lev(path, file, var, threshold, cubulation):
+def _field_icon_lev(path, file, var, threshold, cubulation):
     
     # field on triangular grid
     field = xr.open_dataset(path + file)[var].squeeze().values
@@ -116,4 +116,4 @@ def __field_icon_lev(path, file, var, threshold, cubulation):
             cube = entry[1]         # cube coordinate
             field_cube[lev, cube[0], cube[1], cube[2]] = field[lev, triangle]
     
-    return field, field_cube
+    return field, field_cube
\ No newline at end of file