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Approximating Angles

H

ERE’S A SURPRISINGLY ACCURATEprocedure to estimate angles
using only a rule and a compass. First, draw a circle with a
radius of 5^3 ⁄ 4 in. Let’s assume you want a 10º angle. Mark off two
points 1 in. apart (a 1-in. chord) on the circumference. Join the two
points with the center of the circle, and the resulting angle is almost
exactly 10º. If you want 20º, just lay out two 1-in. chords (not one
2-in. chord). For angles less than 10º, use fractions of an inch or just
split the distance by eye. For large angles, lay out multiples of 60º
(using the compass set to the circle’s radius) then add or subtract 1-in.
(10º) slices to get the angle you want.
—JULESPAQUIN,Laval, Que.,Canada

MEASURING, MARKING & LAYOUT

Draw circle,

radius: 5^3 ⁄ 4 in.

Mark off

1-in. chord.

Connect to cen-

10°