diff --git a/Overlap/report_graph.py b/Overlap/report_graph.py
index 0797c026cf2bc2e282b3efcddfc2145c3676be92..c414908fd8f3c6d81260db68d849adeab95a1503 100755
--- a/Overlap/report_graph.py
+++ b/Overlap/report_graph.py
@@ -1,5 +1,11 @@
 #!/usr/bin/env python3
 
+"""Note that this script loads the whole graph into memory, with
+networkx, even with option --node. For the global graph on 28 years,
+this requires about 13 GiB of main memory.
+
+"""
+
 from os import path
 import os
 import json
@@ -15,6 +21,7 @@ def read_eddy_graph(edgelist, shpc_dir=None, orientation="Cyclones"):
         G = nx.read_edgelist(edgelist, create_using=nx.DiGraph, nodetype=int)
         dir_edgelist = path.dirname(edgelist)
         e_overestim_file = path.join(dir_edgelist, "e_overestim.txt")
+
         with open(e_overestim_file) as f:
             G.graph["e_overestim"] = int(f.read())