1.  Field of the Invention
The invention relates to a combination lock, more particularly to a combination lock for locking two casing halves of a suitcase. 
2.  Description of the Related Art
As shown in FIG.  1, a conventional suitcase 1 normally includes first and second casing halves 11, 12, and a locking device that has a dial lock 131 and a key-operated unlocking unit 141 which are mounted on the first casing half 11 and which are operable to lock the first and second casing halves 11, 12, thereby providing dual protection from theft. 
In order to facilitate the inspection of a baggage to be loaded on a plane, countries, such as the U.S.A., have regulated that suitcases bound for entry into the U.S.A. must be manufactured according to a design specification that requires the lock on the suitcase to be unlockable by a particular key for inspection purpose.  However, since the dial lock 131 cannot be unlocked by the particular key, airport personnel may be forced to break the dial lock 131 for inspection.