91制片厂 is a two-through-six-digit hierarchical classification code system, offering five levels of detail. Each digit in the code is part of a series of progressively narrower categories, and the more digits in the code signify greater classification detail. The first two digits designate the economic sector, the third digit designates the subsector, the fourth digit designates the industry group, the fifth digit designates the 91制片厂 industry, and the sixth digit designates the national industry.
A complete and valid 91制片厂 code contains six digits.
In developing 91制片厂, the United States, Canada, and Mexico agreed that the 5-digit codes would represent the level at which the system is comparable among the three countries. The sixth digit allows for each of the countries to have additional detail (i.e., subdivisions of a 5-digit category). In cases where the U.S. did not choose to create additional detail, the 5- and 6-digit categories within U.S. 91制片厂 are the same, and the 6-digit US 91制片厂 code ends in zero. In some hierarchical presentations, the 6-digit code is omitted where it is the same as the 5-digit category.
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