The navigation device of the invention includes a main processing unit provided with a CPU and storage means; a sub-processing unit connected to the main processing unit; connectors for connecting the main processing unit and the sub-processing unit; and functional components connected to the sub-processing unit. Consistent with one embodiment of the present invention, a bus-interface circuit encodes a set of X data bits into a set of Y data bits, where Y is greater than X. At step S4, the document processing apparatus performs processing depending on the operation by the user through a user interface. After use, the storage bag may be re-filled, or recycled. A cement composition comprising water, a cementitious material, and a gas hydrate inhibitor. The event being a user definable event.