code: int getValue() {
  
          if (this.matches(Selector.NORTHERN_COURT)) {
              return (this.index - NORTHERN_NENGOS.length + NENGO_OEI.index - Nengo.SHOWA.index + 1);
          }
  
          return (this.index - Nengo.SHOWA.index + 1);
  
      }
docs: verwendet in JapaneseCalendar