Otis King's patent calculator in case (a spiral logarithmic slide rule) Otis King's patent calculator in case (a spiral logarithmic slide rule) 1923
Otis King pocket calculator (a spiral logarithmic slide rule), Model K, in box with instructions Otis King pocket calculator (a spiral logarithmic slide rule)
Spiral slide rule "R.H.S. Calculator" made by Steward, with descriptive booklet; size of rule 11 1/2" long by about 7/8" diameter, metal, with paper scale Spiral slide rule "R.H.S. Calculator" made by Steward