A dial tone generator outputs a particular dial tone to a party to indicate that a call block feature is enabled for the party. The ink supply step supplies ink to a common flow-passage in the state in which movement of the ink inside a second ink-flow passage is tolerated with an inflow side valve, and movement of the ink inside a third ink-flow passage is restricted with an outflow side valve. The system further includes an apparatus for detecting the AC voltage applied between the electrodes, thus forming an AC voltage reference. The method and system uses human perception techniques to weight the feature vectors.