anchor.diff:  
   (let ((%classes% (make-array 7 :fill-pointer 0))
         (%classes-lock% (make-lock "%CLASSES%")))
  -  ;; FIXME: lock %classes% #THREADSAFETY
     (defun register-measurement-class (c)
       (with-lock-held (%classes-lock%)
         (let* ((s (measurement-symbol c))
  
positive.code: 
  
  
  ;; FIXME: does not work in SBCL, but should.
  ;;
  ;; In macroexapansion for DEFBOUNCE%, NAME is said to be unbound
  ;;
  
negative.code: 
     
  
  #+SBCL ;; FIXME: also port to other impmls. using PCL
  (defmethod sb-mop:validate-superclass ((class measurement-class)
                                         (superclass standard-class))
    (values t))
  