=16.= In all classes of accounting records, the unit system is rapidly gaining in popularity. The unit system, so called, consists of individual records of each transaction or each item recorded, instead of a combination of several transactions in one record. The increase in the use of the unit system has been brought about very largely by the improvements in typewriters, which make it possible to produce several copies of a given document at one writing. An example of the application of the unit idea is seen in modern sales records, where duplicate invoices are made, one copy serving as a sales sheet and posting medium. [Illustration: A VIEW IN THE GENERAL OFFICES OF THE S. OBERMAYER CO., CINCINNATI, OHIO] The unit system has been very successfully applied to voucher accounting, saving much time and resulting in very complete records. Compared with ordinary voucher systems, the most prominent feature of the unit system is a method of distribution by filing, rather than by means of a voucher register. All vouchers are made on the typewriter, in manifold, one or more copies being used for record purposes only. The original is used exactly as described in the preceding pages. An essential feature of the system is that a copy of the voucher is provided for each account to which it is to be distributed. When one account only is involved, the voucher is made in duplicate, but if the amount is to be distributed to two accounts an extra copy is required. The voucher should be so arranged that the distribution can be shown on the face of the duplicate and triplicate copies. The duplicate voucher is filed according to its distribution, instead of recording the amount in the voucher register. A vertical file is used for this purpose. The index cards are headed with the names of the accounts, and are arranged in the order of the accounts in the ledger; this being the order in which the same accounts would be arranged in a voucher register. Back of each index is a folder in which the vouchers are filed. Each voucher copy is filed in the folder representing its proper account, and is securely fastened to the folder with a staple or paper fastener. When this voucher is filed it is also recorded on the outside of the folder, which is printed as shown in Fig. 18. This form is designed for a record of amounts, distributed under the proper monthly headings. The amount of each voucher is carried to the current month's column. At the end of the month, the footing of the column shows the amount to be charged to that particular account in the general ledger.