In the system referred to, eight colors are used. Seven of these represent occupations of prospective customers, while the eighth is used for customers. A manager or executive officer is represented by a blue card, a sales manager by a white card, etc. When a prospect becomes a customer, the card is removed from the follow-up file, the amount of the sale is entered on the back, and it is placed in another file reserved for customers. At the same time a red card is placed in the follow-up file for use in further circularizing. The tab on the customer's card shows his business, but the occupation is not so important since he is already acquainted with the house and its goods. A more familiar tone can be adopted in letters to a customer, than to a prospect. A complete classification, such as provided in this system, is of immense value to a letter salesman. Suppose he wishes to address all executives--the blue card is used; if he wants to reach customers who are manufacturers, red cards with No. 1 tabs are the ones used. He can make his letter fit a particular class and be sure of the class. =Classification of Sales.= There are certain lines of business in which a second order for the same article is seldom received from any customer. An example is the music business. The chances of selling a customer a second piano are remote, but the fact that he has purchased a piano is a sure indication that he will be interested in certain classes of music. Book publishing is another example. A man who buys a book on advertising, or commercial law, or auditing is quite likely to be a buyer of other books on the same or kindred subjects. [Illustration: Fig. 30. Card for a Classified Record of Purchases] In a business conducted through the mail, a classified sales list that shows at a glance what classes of goods have been sold to each customer furnishes an excellent guide for further circularizing. On such records it is not necessary to show the amounts of purchases--the class is the important item. Fig. 30 shows a card used for a record of this kind. The goods are divided into four classes, indicated by the letters at the head of the columns. When the first sale is made, the name and address are entered on one of these cards, and the date indicated in the proper column. A movable tab is placed on the upper edge of the card, over the letter that indicates the class, and the card is filed. As subsequent purchases are made the dates are entered, and if the purchase includes another class of goods, another tab is placed on the card. In time, one card may bear four tabs, indicating that the customer has bought goods in all four classes. When new goods are received, they can be brought to the notice of those customers whose purchases indicate that they are most likely to be interested, without disturbing the other cards.