A scale of chords may be used to set or read an
angle
In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the '' vertex'' of the angle.
Angles formed by two rays lie in the plane that contains the rays. Angles a ...
in the absence of a
protractor. To draw an angle, compasses describe an arc from origin with a radius taken from the 60 mark. The required angle is copied from the scale by the compasses, and an arc of this radius drawn from the sixty mark so it intersects the first arc. The line drawn from this point to the origin will be at the target angle.
Mathematics
A
chord is a line drawn between two points on the
circumference
In geometry, the circumference (from Latin ''circumferens'', meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out t ...
of a circle. Look at the centre point of this line. For a circle of radius , each half will be
so the chord will be
. The line of chords scale represents each of these values linearly on a scale running from 0 to 60.
Availability
It appears on
Gunter's scale and the Foster Serle
dialing scales. The commercial company Stanley marketed a metal version (Stanley 60R Line of Chords Rule) in 2015.
See also
*
Ptolemy's table of chords
The table of chords, created by the Greek astronomer, geometer, and geographer Ptolemy in Egypt during the 2nd century AD, is a trigonometric table in Book I, chapter 11 of Ptolemy's ''Almagest'', a treatise on mathematical astronomy. It ...
References
;Notes
;Bibliography
*
Angle
Scientific instruments
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