Office supplies are all the supplies regularly used in offices by businesses and other organizations. It includes small, expendable, daily use items such as paper clips, post-it notes, and staples, small machines such as hole punches, binders, staplers and laminators, writing utensils and paper, but also encompasses higher-cost equipment like computers, printers, fax machines, photocopiers and cash registers, as well as office furniture such as chairs, cubicles, filing cabinet, and armoire desks. Two very common[citation needed] medium-to-high-cost office equipment items before the advent of suitably priced word processing machines and PCs in the 1970s and 1980s were typewriters and adding machines.Many businesses in the office supply industry have recently expanded into related markets[citation needed] for businesses like copy centers, which facilitate the creation and printing of business collateral such as business cards and stationery, plus printing and binding of high quality, high volume business and engineering documents. Some businesses also provide services for shipping, including packaging and bulk mailing. In addition, many retail chains sell related supplies beyond businesses and regularly market their stores as a center for school supplies with August and early September being a major retail period for Back to school sales.The office supply industry was estimated to be worth US$ 225 billion in 1999 and is still growing.