anchor.diff:    (rescale scalar (prefix-degree prefix)))
   
   
  -
   (defmethod nrescale ((scalar measurement) (prefix fixnum))
     (multiple-value-bind (new-mag new-deg) 
         (shift-magnitude (measurement-magnitude scalar)
  
positive.code:   ()
    (:report
     (lambda (c s)
       (format s "No measureent prefix registered for name ~S"
               (entity-not-found-name c)))))
  
  (define-condition prefix-degree-not-found (entity-not-found)
    ()
    (:report
     (lambda (c s)
       (format s "No measureent prefix registered for degree ~S"
               (entity-not-found-name c)))))
  
  
  
negative.code:   ()
    (:report
     (lambda (c s)
       (format s "No measurement class registered for name ~S"
               (entity-not-found-name c)))))
  
     
  