anchor.diff:  
   (defvar *flops-per-interaction* 20)
   
  -(defun compute-perf-stats (num-bodies fps iterations)
  -  (let* ((interactions-per-second (/ (* num-bodies num-bodies iterations)
  -                                     (/ 1.0 fps)
  -                                     1.0e9))
  -         (gflops                  (* interactions-per-second *flops-per-interaction*)))
  +(defun compute-pref-stats (counter num-bodies interactions)
  +  (let* ((interactions-per-second
  +           (/ (* num-bodies num-bodies interactions)
  +              (/ 1.0 fps)
  +              1.0e9))
  +         (gflops (* interactions-per-second *flops-per-interaction*)))
       (values interactions-per-second gflops)))
   
  -(let ((fps-count 0)
  -      (fps-limit 5)
  -      (template "CUDA N-Body (~A bodies): ~,1F fps | ~,1F BIPS | ~,1F GFLOP/s | single precision~%"))
  -  (defun display-framerate (num-bodies fps)
  -    (incf fps-count)
  -    (when (>= fps-count fps-limit)
  -      (multiple-value-bind (interactions-per-second gflops)
  -          (compute-perf-stats num-bodies fps 1)
  -        (format t template num-bodies fps interactions-per-second gflops)
  -        (glut:set-window-title (format nil template num-bodies fps interactions-per-second gflops)))
  -      (setf fps-count 0
  -            fps-limit (max fps 1.0)))))
  +(let ((previous 0.0))
  +  (defun display-framerate (counter num-bodies)
  +    (let ((fps (fps-counter-fps counter)))
  +      (when (/= fps previous)
  +        (setf previous fps)
  +        (multiple-value-bind (interactions-per-second gflops)
  +            (compute-pref-stats counter num-bodies 1)
  +          (let ((msg (format nil "CUDA N-Body (~A bodies): ~,1F fps | ~,1F BIPS | ~,1F GFLOP/s | single precision~%"
  +                           num-bodies fps interactions-per-second gflops)))
  +            (format t msg)
  +            (glut:set-window-title msg)))))))
   
   
   ;;;
  
positive.code:     ;; swap buffers
      (glut:swap-buffers)
      ;; display frame rate
      (measure-framerate counter)
      (display-framerate (nbody-demo-num-bodies nbody-demo)
                         (get-framerate counter))))
  
  (defmethod glut:reshape ((w nbody-window) width height)
    ;; configure on projection mode
  
negative.code:   (timer :timer :read-only t)
    (fps-count 0)
    (fps-limit 5)
    (fps 0.0))
  
  (defun init-framerate-counter ()
    (let ((timer (create-timer)))
  