docs: def minimum( self ):
          """
          Returns the minimum value for this ruler.  If the cached value is None,
          then a default value will be specified based on the ruler type.
          
          :return     <variant>
          """
          if ( self._minimum is not None ):
              return self._minimum
          
          rtype = self.rulerType()
          
          if ( rtype == XChartRuler.Type.Number ):
              self._minimum = 0
              
          elif ( rtype == XChartRuler.Type.Date ):
              self._minimum = QDate.currentDate()
          
          elif ( rtype == XChartRuler.Type.Datetime ):
              self._minimum = QDateTime.currentDateTime()
          
          elif ( rtype == XChartRuler.Type.Time ):
              self._minimum = QDateTime.currentDateTime().time()
          
          else:
              notches = self.notches()
              if ( notches ):
                  self._minimum = notches[0]
          
          return self._minimum