Scope and ContentManual: The Polyphase Duplex Slide Rule. A Self Teaching Manual... by William E. Breckenridge. Published by Keuffel & Esser Co., New York & Hoboken, N.J., [1924]. Booklet, 5-1/4" x 8" high, pp [ii], 90. Two copies; one copy lacking original cover (a salmon colored stiff printed paper.) Manual was for the model no. 4088-3 slide rule. Copyright date and issue date are not necessarily the same.