After the bills have been sent out, the duplicates are filed away. The best known way to file them is alphabetically; each customer's bill for the various months together. This is in contrast to the plan of filing each month's bills away separately. If it is wished to refer to any one person's charges for a given number of months it is necessary, under the latter plan, to refer to several binders. [Illustration: Fig. 27. Remington Billing Machines ] One of the devices which did more to permit cylinder machines to do billing successfully is shown in Fig. 26. Formerly, when two or more sheets of paper were inserted in a cylinder machine, the small feed roll which rests against the large rubber platen, fed the under papers at a different speed than those sheets which rested against the large roll. The result was that the papers were fed unevenly into the machine. When removed, it was impossible to replace them in the same relation in which they were before. The device illustrated furnishes a resting place for evenly placing all the sheets in the machine by pressing a release lever which draws the feed rolls away from the large roll until the papers or sheets are properly placed in the machine. Started evenly, they will invariably feed evenly. [Illustration: Fig. 28. Smith Premier Dry Goods Billing Machine ] This is of particular advantage in retail dry goods billing, where a sheet is placed in and out of a machine as many as thirty times a month. If the top of the bill is each time started from the same starting point, namely, the top of the statement, it will feed correctly to the next writing point on the statement without any adjustment. The Remington, Fig. 27, and Underwood machines are equipped with devices for the same purpose. The Smith Premier, Fig. 28, and the Elliott-Fisher machines are equipped with rolls of carbon which automatically manifold folded monthly bill forms. DEVICES OF THE FUTURE One of the successful devices which is being perfected at this time is a combination of an adding machine and a cylinder billing machine which can be operated as a combined machine or separately as two machines, and may be actually removed, one from another. The idea is to have a platen or roll which can act as shuttle between the typewriter and the adding machine. By pressing a button, the roll travels from the typewriter to the adding machine. This scheme has the same advantage as has the farmer who can operate his horses singly or in pairs. The adding machine people have been experimenting and gradually increasing the printing capacity of their machines. They are now able to print the different months of the year and some other abbreviations for monthly statement work. Further developments can be expected along this line. Adding machines which list are a very important factor in office work and their capacity is so large for certain classes of work that space does not permit of detailed treatment here.