| 摘要 |
Each of a plurality of connected optional apparatuses includes a sliding member slidable in a direction of connection, and a display provided in the sliding member, the display having a plurality of unique identifiers. The sliding member is movable while contacting a sliding member of an adjacent one of the plurality of optional apparatuses, and when the plurality of optional apparatuses are connected, a moving amount of a sliding member of each of the plurality of optional apparatuses differs, and therefore displays a different unique identifier.
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