diff --git a/DiffractionGratings/grating3D_data_hole.geo b/DiffractionGratings/grating3D_data_hole.geo
index 51f9e57f1c27d56114c74cc66582fb4d741c6413..144ef9fd560e541cd1daef1af32fc3fabc4a6d9e 100644
--- a/DiffractionGratings/grating3D_data_hole.geo
+++ b/DiffractionGratings/grating3D_data_hole.geo
@@ -2,6 +2,7 @@
 // Ndofs 1116912
 // solve wall time mumps  : 634.318s - R00=0.2432916553175037
 // solve wall time pastix : 966.046s - R00=0.2432916553175064
+// beware : very near a Rayleigh anomaly
 
 nm  = 1000;
 pp1 = "1Incident Plane Wave";