diff -r 02c0b94f74e7 -r e1193f875c8c src/base/statistics.hh
--- a/src/base/statistics.hh	Tue Aug 27 08:30:41 2013 -0500
+++ b/src/base/statistics.hh	Tue Aug 27 08:30:47 2013 -0500
@@ -2856,6 +2856,14 @@
      * @return a reference to this formula.
      */
     const Formula &operator+=(Temp r);
+
+    /**
+     * Divide the existing tree by the given one.
+     * @param r The root of the expression tree.
+     * @return a reference to this formula.
+     */
+    const Formula &operator/=(Temp r);
+
     /**
      * Return the result of the Fomula in a vector.  If there were no Vector
      * components to the Formula, then the vector is size 1.  If there were,
diff -r 02c0b94f74e7 -r e1193f875c8c src/base/statistics.cc
--- a/src/base/statistics.cc	Tue Aug 27 08:30:41 2013 -0500
+++ b/src/base/statistics.cc	Tue Aug 27 08:30:47 2013 -0500
@@ -387,6 +387,16 @@
     return *this;
 }
 
+const Formula &
+Formula::operator/=(Temp r)
+{
+    assert (root);
+    root = NodePtr(new BinaryNode<std::divides<Result> >(root, r));
+
+    assert(size());
+    return *this;
+}
+
 void
 Formula::result(VResult &vec) const
 {