anchor.diff:  
   ;; (scalar-magnitude (convert-measurement (make-measurement (rational pi) :|rad|) :|deg|))
   ;; => 180
  +
  +;;; %% Dimensionless Measure
  +
  +(defclass dimensionless-measure (measurement-class)
  +  ()
  +  (:documentation "Informal domain for dimensionless measures")
  +  (:metaclass measurement-domain)
  +  ;; FIXME: #I18N
  +  (:print-name . "dimensionless measure")
  +  (:print-label . "dimensionless measure")
  +  (:symbol . :dimensionless-measure)
  +  (:base-measure . unity))
  +
  +(register-measurement-domain (find-class 'dimensionless-measure))
  +
  +(defclass unity (measurement)
  +  ()
  +  (:documentation "Informal base measure of dimensionless measures")
  +  (:metaclass angular-measure)
  +  (:print-name . "unity")
  +  (:print-label . "u")
  +  (:symbol . :|u|))
  +
  +(register-measurement-class (find-class 'unity))
  +
  +
   
   #| Topic: Measurement Formulas
   
  
positive.code:   ;; FIXME: #I18N
    (:print-name . "angular measure")
    (:print-label . "angular measure")
    (:base-measure . radian))
    
  
  (defclass radian (measurement)
    ()
  
negative.code: 			 :source-unit source-unit
  			 :destination-unit dest-unit
  			 :magnitude factor-magnitude
  			 :exponent factor-exponent)))
  
  
  (defgeneric find-conversion-factor (source-unit dest-unit domain)
  