=Loose-Leaf Sheets with Invoices in Blanket Form.= In some lines of business it is possible to use invoices of equal size. Some firms therefore have the invoices and sales sheets of equal size. The top sheet is perforated horizontally at equal distances, which permits the invoices to be torn apart so that one blanket of form invoices may be separated into three or four separate invoices. This plan can be used where the work is done on an ordinary letter-writing machine. In preparing the papers for billing, a sheet of carbon equal in size to the sales sheet is used. A heavy-weight carbon (10lb.) with hard finish is the best kind of carbon to use for this work. If an extra sales sheet is needed for any purpose, a duplicate sheet of paper, preferably of another color, can be used with another sheet of carbon interleaved between the two sales sheets. This method is wasteful of space as far as the sales sheet is concerned. If each invoice were loose and placed in the machine in such a manner that the first written line on the invoice would be two or three spaces only below the last item of the previous invoice manifolded on the sales sheet, generally _one more_ invoice of average size could be manifolded onto the sales sheet. =Loose-Leaf Sales Sheet with Separate Invoices.= This combination is made possible by the billing machine, the flat-bed and the cylinder style. Cylinder billing machines are equipped with special carriages having special feed rolls which hold the sales sheet until it is fed entirely through the machine. Cylinder machines also have an independent feed roll which can be released by a special lever. This permits an invoice to be inserted in the machine, and then clamped into position by the intermediate feed roll and fed through the machine with the sales sheet until the invoice is completed. The intermediate feed roll is then released, and the invoice removed without disturbing the sales sheet. The next invoice is then placed in position, and the same operation is repeated. This allows one invoice to be manifolded very nearly under the previous invoice. Some firms having invoices of one or two items only, which permits of from seven to nine invoices being manifolded on each page, have the invoices made up in blanket form; that is, seven or eight invoices to a strip. After each invoice is manifolded they advance the next invoice into position and then tear the invoices apart as previously described.