Compares two values based on the notches and values for this ruler.
        
        :param      a | <variant>
                    b | <variant>
        
        :return     <int> 1 || 0 || -1

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)