Vintage '40-'60 Otis King Slide Rule Calculator Scale 423 & 414 Patent 183723. 
Otis Carter Formby King, an electrical engineer in London, invented the “Otis King’s Patent Calculator,” a cylindrical slide rule with helical scales, that was produced by Carbic Ltd. from 1922 to 1972. 
The calculator uses concentric telescoping metal cylinders with a continuous long spiral logarithmic scale. This cylindrical design increases the length of the scales, thereby improving the accuracy relative to the linear type
Still in good conditions, scales clearly legible and not stained, light signs of corrosion on the sliding cylinder.
Repro of original manual enclosed.