The usual routine in numerical filing is first to place the folder numbers on the letters, and then file according to these numbers without reference to the name. Naturally, the file clerk commits to memory the numbers of a large part of the active correspondents, and places them on the letters without referring to the card index. Memory is ever fickle, and if the wrong number is placed on the letter, it is probable that it will be filed accordingly. In the use of figures, the most common of all errors is transposition, and this is a constant source of danger in filing. Suppose, for example, that in placing the number on a letter from the Norton Machine Company, a transposition is made and the number reads _160_ instead of _610_. The letter is filed in folder _No. 160_, just four hundred and fifty folders out of the way. The letter is practically lost, for there is no way to locate it except to look through all of the folders until it is found. With the alphabetical index there is some danger of filing a letter in the wrong place, but it is materially lessened by the fact that the name must be kept in mind. If the letter is incorrectly filed, it probably will be placed in a folder close to the right one. Almost without exception, it will be found within two or three folders of its proper place; there is scarcely a possibility that a letter from Norton will be filed in White's folder. MISCELLANEOUS FILING =Salesmen's Correspondence.= The correspondence from salesmen and branch houses is, as a rule, more bulky than that from even the largest customers. A sub-divison should be provided that will make it possible to locate quickly a letter of any date, without looking through a great mass of correspondence. The most simple way to accomplish this is to divide the correspondence of each salesman or branch by months. A folder should be used each month. Sufficient space should be provided in the general files to hold salesmen's correspondence for an entire year. If subdivided by months, old correspondence can be located much more quickly than if scattered through several transfer files. One way to reduce the bulk of this correspondence in the salesmen's folders is to require each salesman to use a separate sheet for each subject about which he writes. Nine out of every ten letters from a salesman refer specifically to transactions with certain customers, and are chiefly important in connection with the correspondence of those customers. Such letters should be filed in the customers' folders, where they will be found when it is wished to investigate transactions with a customer. The correspondence of some very large customers is also quite bulky. This, also, can be subdivided by the use of a new folder each month. A similar plan is used to advantage in connection with subject filing, a separate folder, filed back of the subject guide, being used for each correspondent.