William Oughtred published his design for a slide rule in 1632. A series of designs followed. In 1727 Jacob Leupold published his Theatrum Arithmetico-Geometricum1 of which Table XII (page 241) is held in this collection (see below).2
This page shows three existing designs for logarithmic proportional rules. The top most (titled Mechanische Rechen Kunst and bearing also the initials MLBMC of its maker) is effectively a Gunter scale and dividers would be used to perform multiplications or divisions using the scale.3 The lower two are very early designs of slide rules.
1 A scanned version of this book may be downloaded from http://ia600304.us.archive.org/33/items/theatrumarithmet00leup/theatrumarithmet00leup.pdf (viewed 3 Jan 2012) (↑)
2 This page was held in a German family and placed on auction on ebay in January 2012, after the seller’s grandfather, an art collector, who had held it and had it restored, passed away. (↑)
3 a diagram of this 
is shown at “Rechenschieber mit logarithmischen Skalen” http://www.rechenwerkzeug.de/staebe.htm (viewed 2 Jan 2012) (↑)
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