anchor.diff:  
   ;;; %% Angular Measure
   
  -(defclass angular-measure (measurement-class)
  +(defclass plane-angle (measurement-class)
     ()
     (:metaclass measurement-domain)
     ;; FIXME: #I18N
     (:print-name . "angular measure")
     (:print-label . "angular measure")
  -  (:symbol . :angular-measure)
  +  (:symbol . :plane-angle)
     (:base-measure . radian))
   
  -(register-measurement-domain (find-class 'angular-measure))
  +(register-measurement-domain (find-class 'plane-angle))
   
   (defclass radian (measurement)
     ()
  -  (:metaclass angular-measure)
  +  (:metaclass plane-angle)
     (:print-name . "radian")
     (:print-label . "rad")
     (:symbol . :|rad|))
   
   (register-measurement-class (find-class 'radian))
   
  -;; (object-print-name (measurement-domain-base-measure (find-class 'angular-measure)))
  +;; (object-print-name (measurement-domain-base-measure (find-class 'plane-angle)))
   ;; => "radian"
   
   (defclass degree (measurement)
     ()
  -  (:metaclass angular-measure)
  +  (:metaclass plane-angle)
     (:base-factor . #.(/ (rational pi) 180) )
     (:print-name . "degree")
     (:print-label . "deg")
  
positive.code:       (md-c (find-class 'measurement-domain))
        (mc-c (find-class 'measurement-class))
        (m-c (find-class 'measurement))
        #+SBCL (src (sb-c:source-location)))
    (labels ((do-def (domain domain-name class print-name print-label name)
  	     (let* ((d 
  
negative.code: 		(multiple-value-bind (d c)
  		    (do-def domain domain-name class print-name print-label  name)
  		  (cons d c))))
              ;; N.B: With regards to normalization of compound unit
              ;; expressions, the set of measurement units defined with
              ;; this form may be stored in a seperate, constant
              ;; (stack allocated) vector of SI base units. The order of
              ;; storage of measurement units within that vector will be
              ;; significant, and must correspond with section 2.1.2 of 
              ;; http://www.bipm.org/en/publications/si-brochure/
              ;;
              ;; Considering the possibly appolications of an "SI Units"
              ;; vector, as such: 
              ;; * The "SI Units" vector may be applied for a normal
              ;;   ordering of elements within compound unit expressions
              ;; * Not only the previous, but the "SI Units" vector may
              ;;   also be aplied in normalization of _partially
              ;;   normalized_ compound unit expressions (e.g. `W A^-1`)
              ;; See also: Documentation, section "Compound unit
              ;; expressions" 
  	    '((length "length" meter "metre" "m" :|m|)
  	      (mass "mass" kilogram "kilogram" "kg" :|kg|)
  	      (time "time, duration" second "second" "s" :|s|)
  