On the back of the customer's card a form similar to Fig. 28 should be printed. This is intended for a record of the purchases of the customer and provides for a monthly record, covering a period of five years. The amount of purchases is entered monthly from the ledger. In a business in which the purchases of each customer are infrequent, each order should be entered with the date, in place of the monthly summary. _Classification of List._ The value of a list of customers is greatly enhanced by a careful classification of the names. Lists of those engaged in the different trades and professions can be bought, but no list is so valuable as one made up of the names of those who have answered your advertisements, or with whom you have done business. [Illustration: Fig. 29. Card File for a Classified Customers' List] Most houses sell goods to those in different trades or occupations. A manufacturer may sell different lines, or the same line, to jobbers, retailers, and consumers; a mail order concern may sell to farmers, mechanics, and small retailers; a retailer may sell to men and women. To sell each different line to a different class of people, requires different arguments--a new line of selling talk must be used in each case. While the personal salesman has an opportunity to size up his prospect, and make his argument fit the individual, the letter salesman must fit his argument to a _class_. To drive home the right argument, he must be sure of the class to which his prospect belongs. He cannot hope to form the personal acquaintance of his prospects, but must rely on a proper classification. The classes into which a list of customers and prospects should be divided depends on the nature of the business and the class of goods sold. It might be manufacturers in different lines, the different professions, retailers in several lines, or all of these combined into one list. With a card list, any classification is easily provided. If the number of classes is small--not exceeding seven or eight--the classes can be indicated by the color of the card, a white card being used for one class, blue for another, etc. For a more extensive classification, cards with numbered tabs, as in Fig. 29, are used. It will be noted that there are twelve of these tabs, and that they are numbered from left to right. In the follow-up systems, from which this illustration is taken, each number represents a certain line of business. Suppose that No. 1 represents manufacturers; if all manufacturers on the list are to be circularized, only those names recorded on cards with the No. 1 tab are addressed. Now if the business is one dealing in specialties, it may be that the specialty to be sold will depend on the position held by the prospect--a sales manager will be more interested in a book on sales methods than in one on factory methods. To further classify the list, colors are used.