"Toutechnique" protractor-calculator, (quadrant of transparent plastic material; 6-inch radius) "Toutechnique" protractor-calculator
Unit conversion slide rule and metric unit converter in slide-rule format, plastic, made in 1975 by IWA-Rechenschieberfabrik, Esslingen, West Germany Unit conversion slide rule and metric unit converter in slide-rule format 1975
Three card slide rule ready reckoners by Omaro, Paris: transmission drive calculator, model I.1 (1935); gear-tooth ready reckoner, model T.3 (1932); mild steel ready reckoner, model P.12 (1935) Three card slide rule ready reckoners by Omaro 1935-1939
Selection of four ready reckoners, for assisting the conversion from L.s.d. to decimal currency and from imperial to metric measures. Selection of four ready reckoners 1972-1976