docs: def compareValues( self, a, b ):
          """
          Compares two values based on the notches and values for this ruler.
          
          :param      a | <variant>
                      b | <variant>
          
          :return     <int> 1 || 0 || -1
          """
          if ( self.rulerType() in (XChartRuler.Type.Custom, 
                                    XChartRuler.Type.Monthly) ):
              
              try:
                  aidx = self._notches.index(a)
              except ValueError:
                  return -1
              
              try:
                  bidx = self._notches.index(b)
              except ValueError:
                  return 1
              
              return cmp(aidx, bidx)
          
          return cmp(a, b)