Much of my recent research has focused on proportions underlying classical designs and the tools that allowed tradespeople to solve complex math problems centuries ago without performing complex equations. A tool called the sector has played a pivotal role in that research. The tool comprises hinged sticks engraved with a variety of scales that, coupled with a pair of dividers, enables you to determine an unknown value without having to deal with numerical calculations.

Many trades used them. Now Acer-Ferrous Toolworks (in collaboration with Red Rose Reproductions) has tailored this finely crafted version for woodworkers. It comes with laser-cut, anodized aluminum legs engraved with clearly marked scales and a slop-free brass hinge with adjustable friction. After a shallow learning curve, it takes only seconds to use this precision tool for a variety of otherwise head-scratching tasks. All you’ll need is a pair of dividers with tips sharp enough to engage the scales’ pin-size index holes. The sector comes with a brief instruction manual that also refers to further online information and video demonstrations.

P scale determines polygons. The sector has engraved scales paired with small holes to accurately capture the tips of dividers. To draw a polygon, all you need to know is the radius of the circle that surrounds it. From there, you can step off the dividers to draw the shape.

—Jim Tolpin explores the tools and methods of woodworking in centuries past at byhandandeye.com.

Photos: Barry NM Dim

From Fine Woodworking #284

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	Ep 7: Laying out the outside of the bowl In this episode, Dave lays out the outside of the bowl by using a folding ruler as a sector, and of course, more compass work
	Story Poles and How to Use Them APRIL 1, 1994 An ancient measurement tool ensures precise, fail-safe layouts
	Haven for Hand Tools A quiet workshop dedicated to hand tools.