diff --git a/src/Octree.java b/src/Octree.java
index 6003091..229105e 100644
--- a/src/Octree.java
+++ b/src/Octree.java
@@ -55,8 +55,8 @@ public class Octree {
 }
 
 abstract class OctreeItem {
-    protected Vector center;
-    protected double size;
+    protected final Vector center;
+    protected final double size;
 
     protected Body pseudoBody;
 
@@ -76,10 +76,14 @@ abstract class OctreeItem {
 
 class OctreeNode extends OctreeItem {
     private final OctreeItem[] children;
+    private final Vector p1;
+    private final Vector p2 ;
 
     protected OctreeNode(Vector center, double size) {
         super(center, size);
         children = new OctreeItem[8];
+        p1 = center.plus(new Vector(size / 2));
+        p2 = center.minus(new Vector(size / 2));
     }
 
     @Override
@@ -106,7 +110,7 @@ class OctreeNode extends OctreeItem {
         Vector massCenter = new Vector();
         for (OctreeItem oct : children) {
             if (oct == null) continue;
-            massCenter = massCenter.plus(oct.pseudoBody.massCenter().times(oct.pseudoBody.mass() / mass));
+            massCenter.add(oct.pseudoBody.massCenter().times(oct.pseudoBody.mass() / mass));
         }
         this.pseudoBody = new Body(mass, massCenter);
     }
@@ -122,7 +126,7 @@ class OctreeNode extends OctreeItem {
         Vector force = new Vector();
         for (OctreeItem child : children) {
             if (child == null) continue;
-            force = force.plus(child.getForcesOnBody(body, t));
+            force.add(child.getForcesOnBody(body, t));
         }
         return force;
     }
@@ -133,10 +137,12 @@ class OctreeNode extends OctreeItem {
             if (child == null) continue;
             child.draw(cd);
         }
+        /*
         Vector p1 = center.minus(new Vector(size / 2));
         Vector p2 = new Vector(size).minus(new Vector(Simulation.SECTION_SIZE / 2));
         cd.setColor(Color.CYAN);
         cd.drawRectangle(p1.getScreenX(cd), p1.getScreenY(cd), p2.getScreenX(cd), p2.getScreenY(cd));
+        */
     }
 
     private int getOctantNum(Vector bodyPos) {
@@ -146,8 +152,6 @@ class OctreeNode extends OctreeItem {
     }
 
     private boolean isInOctant(Vector pos) {
-        Vector p1 = center.plus(new Vector(size / 2));
-        Vector p2 = center.minus(new Vector(size / 2));
         return  pos.getX() <= p1.getX() && pos.getY() <= p1.getY() && pos.getZ() <= p1.getZ() &&
                 pos.getX() >= p2.getX() && pos.getY() >= p2.getY() && pos.getZ() >= p2.getZ();
     }
diff --git a/src/Vector.java b/src/Vector.java
index 71fa038..ccc21df 100644
--- a/src/Vector.java
+++ b/src/Vector.java
@@ -45,6 +45,12 @@ public class Vector {
         return new Vector(x + v.x, y + v.y, z + v.z);
     }
 
+    public void add(Vector v) {
+        this.x += v.x;
+        this.y += v.y;
+        this.z += v.z;
+    }
+
     /**
      * Returns the product of this vector and 'd'.
      */