diff --git a/src/graphics/buffers.c b/src/graphics/buffers.c
index 603bf92..ec7bfe1 100644
--- a/src/graphics/buffers.c
+++ b/src/graphics/buffers.c
@@ -482,7 +482,7 @@ bool draw_some_arrows (GLuint *lines_origin, long s, long stx, long sty,
 void show_user_choices(long model_size_x, long model_size_y, long model_size_z,
                        GLuint *arrows, int model_arrows_nb, int pref_show_grid)
 {
-    printf("model + user constraints :  space size x,y,z = %ld,%ld,%ld     ", model_size_x, model_size_y, model_size_z);
+    printf("\nmodel + user constraints :  space size x,y,z = %ld,%ld,%ld     ", model_size_x, model_size_y, model_size_z);
     if (model_arrows_nb > 0)         printf("[%d] arrows     ", model_arrows_nb);
 //    if (pref_mark_unit_space == 0)   printf("no unit_space marks     ");
 //    if (pref_mark_unit_space == 1)   printf("first unit space marked     ");
@@ -507,7 +507,7 @@ void show_user_choices(long model_size_x, long model_size_y, long model_size_z,
         printf("[%2d] = %2d,  %2d,  %2d,  %2d,  %2d        \n",\
         i, *(arrows + i * 5 + 0), *(arrows + i * 5 + 1), *(arrows + i * 5 + 2), *(arrows + i * 5 + 3), *(arrows + i * 5 + 4));
 
-    printf("NB   If you play : 'draw_some_arrows(...)' and add some more arrows (in graphics.c below line 571),\
+    if (0) printf("NB   If you play : 'draw_some_arrows(...)' and add some more arrows (in graphics.c below line 571),\
     you must also increase the number of arrows (line 555) \n\
     The 'central_stars_nb' is automatically set equal to the number_of_arrows  (line 559).\n");
 }
diff --git a/src/graphics/graphics.c b/src/graphics/graphics.c
index 5d7c30c..32f4a22 100644
--- a/src/graphics/graphics.c
+++ b/src/graphics/graphics.c
@@ -548,7 +548,7 @@ static void get_model_data_and_user_preferences(){
 
     model_space_size_x = 4;    //   0 < model_space_size_x
     model_space_size_y = 3;    //   0 < model_space_size_y
-    model_space_size_z = 2;    //   0 < model_space_size_z
+    model_space_size_z = 3;    //   0 < model_space_size_z
 
     // XXX ONLY space drawed, no arrows yet
 
@@ -642,9 +642,9 @@ static void compute_buffers_sizes(int model_space_size_x,
 
 //    buffer_lines_size += 16 + 20;  // draw a small cube with diagonals
 
-    buffer_lines_size -= 2;
+//    buffer_lines_size -= 2;
 
-    if (1) printf("allocated buffers sizes  :%4d/3 = %3d vertices, %4d/3 = %3d colors,\
+    if (0) printf("allocated buffers sizes  :%4d/3 = %3d vertices, %4d/3 = %3d colors,\
  %4d/2 = %3d lines, %4d/3 = %3d plans.\n",
                 buffer_vertex_size, buffer_vertex_size / 3,
                 buffer_colors_size, buffer_colors_size / 3,
@@ -659,6 +659,11 @@ static bool rewrite_arrow (GLuint *arrows, long address, long weight,
 {
     printf("write the arrow weight to %ld at (%ld, %ld, %ld, %ld)\n",\
            weight, site, x, y, z);
+
+    *(arrows + address + 0) = weight;
+
+    show_user_choices(model_space_size_x, model_space_size_y, model_space_size_z,
+                      arrows, arrows_nb, pref_show_grid);
     return 1; /* replaces the load of the existing arrow by the load 'weight' */
 }
 
@@ -666,6 +671,20 @@ static bool create_arrow (GLuint *arrows, long weight, long site, long x, long y
 {
     printf("create a new arrow with weight = %ld at (%ld, %ld, %ld, %ld)\n",\
            weight, site, x, y, z);
+
+    arrows_nb ++;
+    buffer_lines_origin = g_realloc(buffer_lines_origin, buffer_lines_size * 2 * sizeof(GLuint) * 2);
+
+    *(arrows + buffer_lines_size + 0) = weight;
+    *(arrows + buffer_lines_size + 1) = site;
+    *(arrows + buffer_lines_size + 2) = x;
+    *(arrows + buffer_lines_size + 3) = y;
+    *(arrows + buffer_lines_size + 4) = z;
+
+    buffer_lines_size += 14;
+
+    show_user_choices(model_space_size_x, model_space_size_y, model_space_size_z,
+                      arrows, arrows_nb, pref_show_grid);
     return 1;
 }
 
@@ -708,6 +727,7 @@ static long check_for_arrow (GLuint *arrows, long site, long x, long y, long z)
         f_z      = *(arrows + i * 5 + 4);
 
         if (f_site == site && f_x == x && f_y == y && f_z == z) {
+            if (f_weight > 1) printf("weight = %ld    ", f_weight);
             address = i * 5;
             printf("found at %ld (%ld / 5 = %ld)\n", address, address, address / 5);
         }
@@ -810,6 +830,13 @@ void graphics_init_buffers(const void *gl_area)
     set_arrow(arrows, 0, 2,  2, 1, 1);
     set_arrow(arrows, 0, 3,  2, 2, 1);
 
+    set_arrow(arrows, 1, 0,  0, 0, 2);
+    set_arrow(arrows, 1, 1,  1, 0, 2);
+    set_arrow(arrows, 1, 2,  0, 0, 2);
+    set_arrow(arrows, 1, 3,  0, 1, 2);
+
+//    set_arrow(arrows, 2, 1,  1, 0, 2);
+
     draw_some_arrows (buffer_lines_origin, s,
                       model_space_size_z * model_space_size_y, model_space_size_z,
                       arrows, arrows_nb);