[no place of publication stated]: [no publisher stated] [no date noted] + April 9, 1953. Throbac I: -5 pages. Throbac - Circuit Operation: -7 pages + 1 plate leaf. 10 7/8 x 8 3/8 inches. Both are typescript carbons on thin paper, printed recto only. Paperclipped upper left. Includes small note: "Thank you for lending this to us. However, our plans have changed & we are thus unable to build a "super modern" Throback. T R Baskhear". Cyanotype plate with ink stamp on rear "Printed Apr 15, 1953 Murray Hill" surrounded by 4 concentric circles. Very Good. Wraps. 
Apparently published only in the Sloane and Wyner bibliography, this paper describes at a high level what THROBAC I is (THROBAC stands for THrifty ROman-numeral BAckward looking Computer) and what it can do. The second paper "THROBAC - CIRCUIT OPERATION" contains a detailed description of the circuit operation, and the plate in the rear is a circuit diagram showing how the pieces interact.
"Throbac...is a relay desk calculator operating entirely in the Roman numeral system. It performs the four operations addition, subtraction, multiplication, and division. The controls and method of operation are very similar to the Marchant desk calculator." (first paragraph)
THROBAC I was constructed and currently resides in the MIT Museum collection. (item 2007.030.011).
"Over the years, Shannon's thinking and nonthinking machines took on a range of shapes and styles. Some served as an oblique social commentary: the 'Ultimate Machine,' when its single switch was flipped, would reach out a mechanical hand and turn itself off. THROBAC ... was a calculator whose keys, processing, and output all worked in Roman numerals, useless except to those who could decipher the difference between, say, CLXII and CXLII. These gadgets had the character of sly, practical jokes. But Shannon also placed a high value on his tinkering. 'The design of game-playing machines may seem at first an entertaining pastime rather than a serious scientific study,' he allowed, ‘but there was a serious side and significant purpose to such work, and at least four or five universities and research laboratories have instituted projects along this line.’" (Soni and Goodman, p. 207)
PROVENANCE: The personal files of Claude E. Shannon (unmarked). The only copy in Shannon's files.
Sloane and Wyner, "Claude Elwood Shannon Collected Papers," #76
Soni, Jimmy, and Goodman, Rob, "A Mind at Play: How Claude Shannon Invented the Information Age," Simon & Schuster: NY, 2017