anchor.diff:  ;;     :initarg :base-scale
   
   
  +;;; %% Derived Measures of Length
  +
   ;; referencing [NIST SP811]
   
   (defclass foot (measurement)
  
positive.code:   (:print-name . "radian")
    (:print-label . "rad")
    (:symbol . :|rad|))
  
  
  (register-measurement-class (find-class 'radian))
  
  
negative.code: (register-measurement-class (find-class 'mile))
  
  
  ;;; %% Angular Measure
  
  (defclass angular-measure (measurement-class)
    ()
    (:metaclass measurement-domain)
  