diff --git a/src/lipyphilic/analysis/memb_thickness.py b/src/lipyphilic/analysis/memb_thickness.py
index ac9834d..83ab30b 100644
--- a/src/lipyphilic/analysis/memb_thickness.py
+++ b/src/lipyphilic/analysis/memb_thickness.py
@@ -169,7 +169,8 @@ def __init__(self, universe, lipid_sel, leaflets, n_bins=1, interpolate=False, r
             of higher-resolution grids. The default is False.
         return_surface : bool, optional
             If True, the height of the bilayer at grid point at each frame is returned as
-            numpy ndarray. The default is False.
+            numpy ndarray. The 2D grid will be stored in self.memb_thickness_grid. The
+            default is False.
 
         Tip
         ---