diff --git a/BloubWorld/mergebloubs.f90 b/BloubWorld/mergebloubs.f90
index 4a63fa7..c230695 100644
--- a/BloubWorld/mergebloubs.f90
+++ b/BloubWorld/mergebloubs.f90
@@ -73,9 +73,17 @@ contains
       type(t_bloubs), intent(in)   :: bla, blb
       type(t_bloubs), intent(out)  :: blr
 
+      real             :: va, vbb
+!-
+! XXX please insert here a static counter for the 'num' id
+!-
+
       blr%nick     = "merged  "
       blr%num      = 0                !    ???
 
+      va = bla%radius * bla%radius * bla%radius
+      vb = blb%radius * blb%radius * blb%radius
+
       blr%px = (bla%px + blb%px) / 2.0
       blr%py = (bla%py + blb%py) / 2.0
       blr%pz = (bla%pz + blb%pz) / 2.0
@@ -84,8 +92,8 @@ contains
       blr%vy = (bla%vy + blb%vy) / 2.0
       blr%vz = (bla%vz + blb%vz) / 2.0
 
-      blr%radius = (bla%radius + blb%radius)
-      blr%age = max(bla%age, blb%age)
+      blr%radius = (va + vb) ** 0.33333333333
+      blr%age = min(bla%age, blb%age)
 
       ! bring it to life !
       blr%alive    = .TRUE.