anchor.diff:    (let ((deg (measurement-degree m))
           (mag (measurement-magnitude m)))
       (multiple-value-bind (mag-adj deg-adj)
  -        (scale-for-si-degree mag deg)
  +        (scale-si mag deg)
         (let ((prefix
                (find deg-adj %prefixes%
                      :key #'prefix-degree
  
positive.code:        (values  (shift-magnitude magnitude scale deg)
                  deg)))))
  
  ;; (scale-for-si-degree 1 5)
  ;; => 100, 3
  ;; (= 1E+05 100E+03)
  
  ;; (scale-for-si-degree 10 5)
  ;; => 1000, 3
  ;; (= 10E+05 1000E+03)
  ;; => T
  
  ;; (scale-for-si-degree 1 -5)
  ;; => 10, -6
  ;;
  ;; (= 1E-05 10E-06)
  ;; => T
  
  ;; (scale-for-si-degree 10 -5)
  ;; => 100, -6
  ;;
  
  
  ;; (scale-for-si-degree 1 -2)
  ;; => 1, -2
  
  ;; (scale-for-si-degree 1 -2 t)
  ;; => 10, -3
  
  
  ;; (scale-for-si-degree 1 2)
  ;; => 1, 2
  
  ;; (scale-for-si-degree 1 2 t)
  ;; => 100, 0
  ;;
  ;; (= (* 1 (expt 10 2)) (* 100 (expt 10 0)))
  
negative.code:              
               (boundp
                (multiple-value-bind (adj-mag deg)
                    (scale-si mag deg)
                    (princ adj-mag stream)
                    (write-char #\Space stream)
                  (unless (zerop deg)
  