An input data correction method and apparatus for a navigation system that has a key filtering function to assist the user to determine possible entries for inputting data. The vacuum is then released with a dry inert gas after drying. Preferably, implementation is in conjunction with communication systems in which wireless communications are conducted between wireless transmit receive units using multiple channels that are concurrently transmitted. The ratchet plate is co-axially affixed to the open-ended split-center shaft, so that when the ratchet turns the open-ended split-center shaft turns through the same rotation.