A modification of the alphabetical system is one in which the catalogues are arranged alphabetically by classes; that is, the lines of goods in which the purchasing agent is interested are divided into specific classes. In each of these divisions, the catalogues of all manufacturers listing that class of goods are arranged in alphabetical order. This method is also very satisfactory for a limited number of catalogues. For a large catalogue file the numerical system will prove the most satisfactory. By this system each catalogue is given a number which should be plainly shown on the back of the catalogue. All catalogues of a specific class are placed in one group, and a series of numbers is set aside for the group. To illustrate, we might have machinery catalogues, numbers 1 to 100. All machinery catalogues would then be given a number in that series. If the number be increased beyond 100, the numbering system would be repeated by using 1_a_, 2_a_, etc. With the numerical system, the catalogues of each group must be arranged in exact numerical order, so that any catalogue may be instantly located. =4. Files.= As has already been stated, the style of file, as well as the method of filing, or indexing, must conform to the conditions in each individual office. However, the experience of the past is the best guide for the future. As a general rule, sectional bookcases will be found the most satisfactory for catalogues in bound form, that is, those with substantial covers, and particularly those that will readily stand on edge. An advantage of the sectional bookcase is that all catalogues can plainly be seen, and even though a numerical system be used, a man soon learns to recognize catalogues of certain manufacturers without referring to any number or indexing system. In every catalogue file will be found pamphlets, circulars, and price lists which are not easily cared for in bookcases. For these a section of a vertical file is recommended, and in many cases this file has been used successfully for filing all sorts of miscellaneous catalogues. It may be expanded to any capacity, and can be used with equal success for either the alphabetical or numerical system of indexing. Which is the better depends upon the circumstances, but in nearly every case either the sectional bookcase or the vertical file, or perhaps a combination of the two, will be found most satisfactory.