JF Ptak Science Books Quick Post
I bumped into this short notice in the magazine Illustrated World for May 1916 and at first didn’t recognize the instrument. It turns out that it is a skeleton drawing of the Ross “Precision Computer”, an 8″, multiple circular spiral (with 25 windings) circular slide rule. It might have had the same effectiveness as a 90′ slide, though I read something elsewhere that it was more like 60′. In any event, it was made of metal, and glass, and celluloid, and was an effective and elegant instrument.
[Illustrated World, May, 1916, page 388. Apologies for the fuzziness–the book was too thick and too old to force it flat on the scanner.]
For more information as well as a photo of the instrument, see the Smithsonian Institution entry here: http://americanhistory.si.edu/collections/search/object/nmah_690756