anchor.diff:  
   (defgeneric measurement-domain-base-measure (instance))
   (defgeneric measurement-domain-symbol (instance))
  +
  +(defgeneric measurement-domain-cf-lock (instance))
  +(defgeneric measurement-domain-conversion-factors (instance))
   
   
   (defclass measurement-domain (pretty-printable-object
  
positive.code: 	(t (vector-push-extend c %domains%)))
        (values c))))
  
  (defun enumerate-measurement-domains ()
    (coerce %domains% 'list))
  
  ;; (find-measurement-domain :electrical-current)
  
  
negative.code:                (when (and (typep c sought-type)
                            (find-slot slot c)
                            (slot-boundp c slot))
                   (return (values (slot-value c slot)
                                   t)))))
             (maybe-inherit-slot (slot sought-type)
  