Washington D.C.: U.S. Army. 1962. Double-sided volvelle with three concentric rings on one side and two on the other, maximum diameter 12,7cm, cream paper printed in red and black, fixed with steel folding tab at center; fine. Rare. An apparent prototype of the ABC-M1A1 RADIAC calculator, which was made in plastic and given to field commanders to calculate the radiation dosage to personnel in a nuclear fallout zone. Similar calculators had been produced for civilian use by William Orr and H. Hunter in the 1950s, but this was intended specifically for military use. Presumably it was superseded by plastic models because of the limited durability of paper.