The names of these buyers of books on medical science and technology topics come from order forms responding to promotions done by mail, fax, email, and print ads in medical journals and magazines. The purchase transactions range from one book to as many as one set of several volumes of reference materials, and the order may amount to as low as USD 40 to as much as USD 2500 for a set of books. Each book buyer's purchases are tracked, hence, it is possible to identify the specific field of specialization in which he is mainly interested.