diff --git a/src/graphics/arrows.c b/src/graphics/arrows.c
index 14ee33a..ddb02fc 100644
--- a/src/graphics/arrows.c
+++ b/src/graphics/arrows.c
@@ -165,11 +165,20 @@ void arrows_write_basis(long offset)
 }
 
 
-static void show_one_arrow_data(int offset_vertex, int offset_colors,
-                float vx, float vy, float vz, float base, float tip)
+static void show_one_arrow_data_1(int offset_vertex, int offset_colors,
+                int space_X, int space_Y, int space_Z,
+                int weight, int site, int x, int y, int z)
 {
-    printf("offset_vertex = %d   vx = %8.5f   vy = %8.5f   vz = %8.5f   base = %8.5f   tip = %8.5f\n",\
-           offset_vertex, vx, vy, vz, base, tip);
+    printf("offset_vertex = %d   offset_colors = %d   weight = %d    site = %d    x,y,z = (%d,%d,%d)\n",\
+           offset_vertex, offset_colors, weight, site, x, y, z);
+}
+
+static void show_one_arrow_data_2(int offset_vertex, int offset_colors,
+                float max, float base, float tip, float ux, float uy, float uz, float vx, float vy, float vz)
+{
+    printf("offset_vertex = %d   max = %8.5f   base = %8.5f   tip = %8.5f\n\
+       ux = %8.5f   uy = %8.5f   uz = %8.5f\n       vx = %8.5f   vy = %8.5f   vz = %8.5f\n",\
+       offset_vertex, max, base, tip, ux, uy, uz, vx, vy, vz);
 }
 
 
@@ -179,6 +188,8 @@ void write_one_arrow(int offset_vertex, int offset_colors, int offset_lines,
                      int space_X, int space_Y, int space_Z,
                      int weight, int site, int x, int y, int z)
 {
+    //  show_one_arrow_data_1 (offset_vertex, offset_colors, space_X, space_Y, space_Z, weight, site, x, y, z);
+
     float nuance = 0.24f,
           max = fmax(space_X, space_Y);
           max = fmax(max, space_Z);
@@ -190,12 +201,16 @@ void write_one_arrow(int offset_vertex, int offset_colors, int offset_lines,
     //    pour qu'elles n'aillent pas jusqu'aux faces des cubes
           arrow_tip_padding = 0.1 * (1 / max),
 
-          vx = (2 * x / space_X - 1) * space_X / max + (1 / max),
-          vy = (2 * y / space_Y - 1) * space_Y / max + (1 / max),
-          vz = (2 * z / space_Z - 1) * space_Z / max + (1 / max);
+          ux = (2 * x) / space_X,
+          uy = (2 * y) / space_Y,
+          uz = (2 * z) / space_Z;
 
-    show_one_arrow_data(offset_vertex, offset_colors,
-                        vx, vy, vz, arrow_basis_width, arrow_tip_padding);
+    float vx = (ux - 1) * (space_X / max) + (1 / max),
+          vy = (uy - 1) * (space_Y / max) + (1 / max),
+          vz = (uz - 1) * (space_Z / max) + (1 / max);
+
+    show_one_arrow_data_2 (offset_vertex, offset_colors, max,
+                        ux, uy, uz, vx, vy, vz, arrow_basis_width, arrow_tip_padding);
 
     //  X - X  axis - central star (basis)
     graphics_write_vertex(vx + arrow_basis_width, vy, vz);