244.54. For the purposes of the rules relating to the application of the rates where one of those rates has been fixed in respect of the category of industrial immovables, each unit of assessment belonging to that category and referred to in subparagraph 2 of the first paragraph of section 244.34 belongs to one of the following classes, according to the percentage that the area of the industrial premises included in the unit or in the aggregate of such premises is of the total non-residential area of the unit
(1) class 1I: less than 25%;
(2) class 2I: 25% or more and less than 75%;
(3) class 3I: 75% or more.
For the purposes of the first paragraph,
(1) “industrial premises” means premises within the meaning of section 244.34 that are mainly intended or used for industrial production purposes;
(2) “non-residential area” means the area of any non-residential immovable within the meaning of section 244.32.