160,186. Anderson, Sir F. J. May 1, 1919. Slide-rules.-Relates to improvements in flat spiral slide rules of the kind described in Specification 22762/03, and comprises an auxiliary circular slide rule to perform a preliminary calculation read off at a lettered and differently marked sector which leads to a similarly differentiated convolution on the large accurate scale. The rim of the large scale is in four quadrants shown by 23 coloured patches at the change a and corresponding to similar markings on the arm C, Fig. 1 , of the slide B. The slide has the convolutions marked alternately with thick and thin lines corresponding to thick and thin marks on the circumference of the " finder," shown in Fig. 2, which sectors are lettered similarly to corresponding portions on the transparent cursor D, Fig. 1 , both for slide and fixed scales. By preliminary calculation on the finder the region for a quantity sought on the large scale is thus quickly found. Clamps are fitted to both cursor and slide arm. Discs are provided as shown in Fig. 3, with square and cube roots for the quantities radially opposite them on the " finder " scale direct and multiplied by 10, 100, and 1000, and are held by a nut h and positioned by a screw pin in an appropriate hole g or g on the base.