The loose-leaf sales sheet and invoice were first used with the flat-bed billing machine, the sales sheet being held in position by being placed over studs (round metal posts), which fitted into the punched holes in the edge of the paper. These punched holes were used ultimately for fitting over the metal binder posts in the loose-leaf binders. The invoices were wider than the regular-size invoice and were perforated about 1 inch or 1½ inches from the left side, as shown in Fig. 8. To the left of the perforated edge were two small holes about 2¾ inches apart, which fitted over two small studs on a sliding bill-holder device. This plan provided a means of holding the large sheet and invoice in proper relation to each other. A piece of carbon paper the same size as the sales sheet was placed between the invoice and the sales sheet. This ruling of the sales sheet is shown in Fig. 9. [Illustration: Fig. 8. Invoice for Use on Billing Machine ] When an invoice was written on the billing machine, it was manifolded on the sales sheet beneath. When the invoice was finished it was ready to mail—no delay in copying invoices, no blurred invoices through careless copying. No fading of the manifolded copy where black carbon paper was used. Inks are not made of indestructible carbons as black carbon paper is made. A condensed billing or invoicing loose-leaf sales book for this purpose is shown in Fig. 10. The following are some of the many good features of the condensed system, as it is in use to-day, briefly stated: [Illustration: Fig. 9. Loose-Leaf Sales Sheet ] Bill and entry in sales book are obtained at one operation. Entries upon sales book agree absolutely with bill rendered. The bill clerk becomes bill and entry clerk combined. There is no danger of a bill being rendered without the proper charge being made. Entries under this system occupy but one-fourth the space required for those written with the pen. There is no waste space upon sales sheet. Both sides of the sales sheet may be utilized. The saving in vault space alone is worthy of special consideration. [Illustration: Fig. 10. Condensed Billing or Invoicing Loose-Leaf Sales Book. _Underwood Typewriter Co._ ]