PATENT CIRCULAR SLIDE RULE (HALDEN CALCULEX) by J. HALDEN & CO.
09-032. English, 2nd quarter 20th century, signed on the front dial "THE HALDEX CALCULEX, PATENT CIRCULAR SLIDE RULE" and embossed on the back plastic disk "DANIEL ADAMSON & Co Ltd, DUKINFIELD." The Calculex consists of two back-to-back dials, each with an outer dial and an inner ring with logarithmic scales engraved on them, protected by plastic discs in a 2 3/8" diameter German-silver ring. The calculator is in very good overall condition and is complete with its original 95 page instruction manual in a folding leather pocket case and the original cardboard box.
