diff --git a/src/graphics/graphics.c b/src/graphics/graphics.c
index 2c3819c..42cea74 100644
--- a/src/graphics/graphics.c
+++ b/src/graphics/graphics.c
@@ -38,9 +38,9 @@ static GLuint *buffer_lines_origin = NULL;
 static GLuint *buffer_plans_origin = NULL;
 
 static volatile int buffer_vertex_size = 0;
-static int buffer_colors_size = 0;
-static int buffer_lines_size = 0;
-static int buffer_plans_size = 0;
+static volatile int buffer_lines_size = 0;
+static volatile int buffer_colors_size = 0;
+static volatile int buffer_plans_size = 0;
 
 
 //  model_data_and_user_preferences :
@@ -56,8 +56,8 @@ static int zzz = 0;
 //  par model_space_size_x, y, z et le nombre de sites
 static GLuint arrows[] = {
       1,    0,    0, 0, 0,
-      1,    1,    0, 0, 0,
-      1,    1,    1, 0, 0,
+      /* 1,    1,    0, 0, 0, */
+      /* 1,    1,    1, 0, 0, */
       /* 1,    2,    0, 0, 0, */
       /* 1,    3,    0, 0, 0, */
       /* 1,    4,    0, 0, 0, */
@@ -82,7 +82,7 @@ static void show_user_choices(int space_size_x,
     if (prefer == 1)    printf("prefer = %d <> show no grid",   prefer);
     if (prefer  > 1)    printf("pref_show_grids = %d",          prefer);
     if (show_all) {
-        printf("\tbuffer_vertex_size = %d\t lines = %d", buffer_vertex_size, buffer_lines_size);
+        printf("\n\t\t\t\t\tbuffer_vertex_size = %d\t buffer_lines_size = %d", buffer_vertex_size, buffer_lines_size);
         if (arrows_nb > 0)  printf("\n   [%2d]   load | site  x    y    z  \n   -------------------------------", arrows_nb);
         for (int i = 0; i < arrows_nb; i++) printf("\n   [%2d] =  %2d  | %2d   %2d   %2d   %2d",\
             i, *(arrows + i * 5 + 0), *(arrows + i * 5 + 1), *(arrows + i * 5 + 2), *(arrows + i * 5 + 3), *(arrows + i * 5 + 4));
@@ -108,10 +108,38 @@ static void get_model_data_and_user_preferences()
 
 
 
-#define DETAIL 0
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 static bool rewrite_arrow (int address, int weight, int site, int x, int y, int z)
 {
-    if (DETAIL) printf("write the arrow weight to %d at (%d, %d, %d, %d)\n",\
+    if (0) printf("write the arrow weight to %d at (%d, %d, %d, %d)\n",\
            weight, site, x, y, z);
 
     *(arrows + address + 0) = weight;
@@ -137,9 +165,9 @@ static bool create_arrow (int weight, int site, int x, int y, int z)
 static bool erase_arrow (int address, int site, int x, int y, int z)
 {
     int arrows_nb = get_arrows_nb();
-    if (1) printf("erase arrow at address %d with values (%d, %d, %d, %d)",\
+    if (0) printf("erase arrow at address %d with values (%d, %d, %d, %d)",\
                   address / 5, site, x, y, z);
-    if (1) printf("      last arrow is  %d, %d, %d, %d, %d\n",
+    if (0) printf("      last arrow is  %d, %d, %d, %d, %d\n",
                    *(arrows + (arrows_nb - 1) * 5 + 0),
                    *(arrows + (arrows_nb - 1) * 5 + 1),
                    *(arrows + (arrows_nb - 1) * 5 + 2),
@@ -163,13 +191,13 @@ static void show_arrows_array (int arrows_nb, int address, int current_weigh, in
 {
     printf("\nset_arrow    (%d  | %2d   %2d   %2d   %2d)   <>   ", weight, site, x, y, z);
 
-    if (arrows_nb == 0 && weight == 0) printf("no arrow in space  +  no arrows to be created  >  end function set_arrow()\n");
-    if (address  == -1 && weight == 0) printf("arrow not found  +  no arrows to be created  >  end function set_arrow()\n");
-    if (address  == -1 && weight  > 0) printf("arrow not found  >  new arrow will be created at line [%d]\n", arrows_nb);
-    if (address  >=  0 && weight == 0) printf("arrow found at line [%d]  >  will be erased\n", address / 5);
+    if (arrows_nb == 0 && weight == 0) printf("buffer_lines : %d\tno arrow in space  +  no arrows to be created  >  end function set_arrow()\n", buffer_lines_size);
+    if (address  == -1 && weight == 0) printf("buffer_lines : %d\tarrow not found  +  no arrows to be created  >  end function set_arrow()\n", buffer_lines_size);
+    if (address  == -1 && weight  > 0) printf("buffer_lines : %d\tarrow not found  >  new arrow will be created at line [%d]\n", buffer_lines_size, arrows_nb);
+    if (address  >=  0 && weight == 0) printf("buffer_lines : %d\tarrow found at line [%d]  >  will be erased\n", buffer_lines_size, address / 5);
     if (address  >=  0 && weight  > 0) {
-        if (current_weigh != weight)   printf("arrow found at line [%d]  >  will be modified\n", address / 5);
-        if (current_weigh == weight)   printf("arrow found at line [%d]  >  will not be modified\n", address / 5);
+        if (current_weigh != weight)   printf("buffer_lines : %d\tarrow found at line [%d]  >  will be modified\n", buffer_lines_size, address / 5);
+        if (current_weigh == weight)   printf("buffer_lines : %d\tarrow found at line [%d]  >  will not be modified\n", buffer_lines_size, address / 5);
     }
 
     printf("   [rank]   load | site  x    y    z\n");
@@ -192,6 +220,25 @@ static void show_arrows_array (int arrows_nb, int address, int current_weigh, in
     }
 }
 
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 static int set_arrow (int weight, int site, int x, int y, int z)
 {
@@ -241,6 +288,43 @@ static int set_arrow (int weight, int site, int x, int y, int z)
 
 
 
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@@ -772,6 +856,7 @@ void main_test_graphics (void)
     if (pref_show_grids > 0) grid_write_ridges (xxx, yyy, zzz);
 
     int offset_after_grids = buffer_vertex_size / 3;
+    int buffer_lines_size_after_cubes = buffer_lines_size;
 
     /* ARROWS */
     arrows_write_terminations (xxx, yyy, zzz);
@@ -797,9 +882,9 @@ void main_test_graphics (void)
         }
     }
 
-    set_arrow (0, 1, 1, 0, 0);
-    set_arrow (0, 1, 0, 0, 0);
-    set_arrow (0, 0, 0, 0, 0);
+    /* set_arrow (0, 1, 1, 0, 0); */
+    /* set_arrow (0, 1, 0, 0, 0); */
+    /* set_arrow (0, 0, 0, 0, 0); */
 
     /* set_arrow (1, 0, 1, 0, 0); */
     /* set_arrow (1, 1, 1, 0, 0); */
@@ -807,11 +892,18 @@ void main_test_graphics (void)
 
     int offset_after_arrows = buffer_vertex_size / 3, difference = offset_after_arrows - offset_after_grids;
 
-    if (1) printf("\nbuffer_vertex_offset_after grids = %d    (x+1)*(y+1)*(z+1) = %d  (x,y,z = %d,%d,%d)",\
+    if (1) printf("\nbuffer_vertex_offset_after grids = %d\t\t(x+1)*(y+1)*(z+1) = %d  (x,y,z = %d,%d,%d)",\
                   offset_after_grids,  (xxx + 1)*(yyy + 1)*(zzz + 1), xxx, yyy, zzz);
-    if (1) printf("\nbuffer_vertex_offset_after arrows = %d   (%d - %d = %d,    %d / 12 <> %d cubes)\n",\
+    if (1) printf("\nbuffer_vertex_offset_after arrows = %d\t\t(%d - %d = %d,    %d / 12 <> %d cubes)",\
                   offset_after_arrows, offset_after_arrows, offset_after_grids,\
                   difference, difference, difference / 12);
+    if (1) printf("\nbuffer_lines_size after cubes = %d\t\t(%d x %d = %d\t%d x %d = %d\t%d x %d = %d\t%d + %d + %d = %d x 2 = %d)",\
+                  buffer_lines_size_after_cubes, xxx+1, yyy+1, (xxx+1) * (yyy+1), xxx+1, zzz+1, (xxx+1) * (zzz+1), yyy+1, zzz+1, (yyy+1) * (zzz+1),\
+                  (xxx+1) * (yyy+1), (xxx+1) * (zzz+1), (yyy+1) * (zzz+1), (xxx+1) * (yyy+1) + (xxx+1) * (zzz+1) + (yyy+1) * (zzz+1),\
+                  ((xxx+1) * (yyy+1) + (xxx+1) * (zzz+1) + (yyy+1) * (zzz+1)) * 2);
+    if (1) printf("\nbuffer_lines_size after arrows = %d\t\t(%d - %d = %d;\t3 + 4 = 7\t7 x 2 = 14\n", buffer_lines_size,\
+                  buffer_lines_size, buffer_lines_size_after_cubes, buffer_lines_size - buffer_lines_size_after_cubes);
+
     if (0) printf("main_test_graphics [ok]\n");
 }