diff --git a/src/OpenFOAM/meshes/polyMesh/polyMeshTetDecomposition/tetIndices.H b/src/OpenFOAM/meshes/polyMesh/polyMeshTetDecomposition/tetIndices.H
index f0dea9aad8bee212f9e328c4ff97c72d4cb7e85a..4eb21b6ac9e46231d69d5018f6cc3cf87ce9b31b 100644
--- a/src/OpenFOAM/meshes/polyMesh/polyMeshTetDecomposition/tetIndices.H
+++ b/src/OpenFOAM/meshes/polyMesh/polyMeshTetDecomposition/tetIndices.H
@@ -28,6 +28,24 @@ Description
     Storage and named access for the indices of a tet which is part of
     the decomposition of a cell.
 
+    Tets are designated by
+    - cell (of course)
+    - face on cell
+    - three points on face (faceBasePt, facePtA, facePtB)
+      When constructing from a mesh and index in the face (tetPtI):
+        - faceBasePt is the mesh.tetBasePtIs() base point
+        - facePtA is tetPtI away from faceBasePt
+        - facePtB is next one after/before facePtA
+        e.g.:
+
+            +---+
+            |2 /|
+            | / |
+            |/ 1|  <- tetPt (so 1 for first triangle, 2 for second)
+            +---+
+            ^
+           faceBasePt
+
 SourceFiles
     tetIndicesI.H
     tetIndices.C