diff --git a/2020/day24/ex1.bash b/2020/day24/ex1.bash
index e3842e9..3247f2b 100755
--- a/2020/day24/ex1.bash
+++ b/2020/day24/ex1.bash
@@ -2,6 +2,10 @@
 #
 # ex1.bash: Advent2020 game, day 24/game 1.
 
+# See https://www.redblobgames.com/grids/hexagons/ for hexagon possible
+# representations.
+# I use the "doubled-coordinate" system here :
+#   https://www.redblobgames.com/grids/hexagons/#coordinates-doubled
 CMD=${0##*/}
 shopt -s extglob
 set -o noglob
diff --git a/2020/day24/ex2.bash b/2020/day24/ex2.bash
index 3edbea9..2ef618f 100755
--- a/2020/day24/ex2.bash
+++ b/2020/day24/ex2.bash
@@ -2,6 +2,10 @@
 #
 # ex1.bash: Advent2020 game, day 24/game 2.
 
+# See https://www.redblobgames.com/grids/hexagons/ for hexagon possible
+# representations.
+# I use the "doubled-coordinate" system here :
+#   https://www.redblobgames.com/grids/hexagons/#coordinates-doubled
 CMD=${0##*/}
 shopt -s extglob
 set -o noglob