To identify whether double perforation stock is A-type or B-type the following general principle applies. Examine the image content for writing of some sort, and if you can read it correctly through the base it is B-type. If you can read it correctly through the emulsion then it is A-type. If no writing is to be found then other classic left to right type images must be sought.
For example women’s jackets and blouses will have buttons on the left side while men’s jackets and shirts will have buttons on the right side. Using this example and the rule above will determine the ‘type’. (Please note that the rules for type identification found under A-type and B-type do not apply to double perforation 16mm, and do not apply at all to 35mm)