anchor.diff:  			:key #'measurement-symbol)))
         (finalize-inheritance %c)
         (cond 
  -	(n (unless (eq (aref %measurement-classes% n) %c)
  -             (simple-style-warning 
  -              "Redfining measurement class for ~S" s)
  -             (setf (aref %measurement-classes% n) %c)))
  +	(n (let ((obj (aref %measurement-classes% n)))
  +             (unless (eq obj %c)
  +               (warn 'measurement-class-redefinition
  +                     :previous-object obj
  +                     :new-object c)))
  +           (setf (aref %measurement-classes% n) %c))
   	(t (vector-push-extend %c %measurement-classes%)))
         (let ((base-ftor (measurement-base-factor %c))
   	    (base-ftor-exp (measurement-base-factor-exponent %c)))
  
positive.code:      (format s "No measurement class registered for name ~S"
               (entity-condition-name c)))))
  
  
  (defclass linear-measurement-class (measurement-class)
    ;; This class is defined, here, for purpose of convenience. 
    ;; See also:  
    ;; `GEOMETRIC-MEASUREMENT-CLASS'
  
negative.code: 
  (defgeneric measurement-base-factor (measurement))
  (defgeneric measurement-base-factor-exponent (measurement))
  ;; ^ FIXME: Clarify applications of those generic functions
  
  ;;; % Measurement Class
  
  