The names of these buyers of books on architectural design come from order forms responding to promotions done by mail, fax, and email, as well as to print ads in architectural journals and magazines. The books covered here are suitable for the advanced learner and the practitioner alike. A purchase transaction can range from one book to as many as several volumes of reference materials on architecture. The order value ranges from as low as USD 50, up to as high as USD 3,000 for a full set of several volumes. Purchases are tracked systematically to identify each buyer’s specific areas of interest within the field of architecture, as well as the recency and frequency of his transactions. Source: specialty book retail outlets and mail order houses.