What is "scale of chords"

Chord \Chord\ (k[^o]rd), n. [L chorda a gut, a string made of a gut, Gr. chordh`. In the sense of a string or small rope, in general, it is written cord. See Cord.]

1. The string of a musical instrument.
   --Milton.

2. (Mus.) A combination of tones simultaneously performed, producing more or less perfect harmony, as, the common chord.

3. (Geom.) A right line uniting the extremities of the arc of a circle or curve.

4. (Anat.) A cord. See Cord, n., 4.

5. (Engin.) The upper or lower part of a truss, usually horizontal, resisting compression or tension.
   --Waddell.

   Accidental, Common, & Vocal chords. See under Accidental, Common, and Vocal.

   Chord of an arch. See Illust. of Arch.

   Chord of curvature, a chord drawn from any point of a curve, in the circle of curvature for that point.

   Scale of chords. See Scale.

Scale \Scale\, n. [L. scalae, pl., scala staircase, ladder; akin to scandere to climb. See Scan; cf. Escalade.]

1. A ladder; a series of steps; a means of ascending. [Obs.]

2. Hence, anything graduated, especially when employed as a measure or rule, or marked by lines at regular intervals. Specifically:

   1. A mathematical instrument, consisting of a slip of wood, ivory, or metal, with one or more sets of spaces graduated and numbered on its surface, for measuring or laying off distances, etc., as in drawing, plotting, and the like. See Gunter's scale.

   2. A series of spaces marked by lines, and representing proportionately larger distances; as, a scale of miles, yards, feet, etc., for a map or plan.

   3. A basis for a numeral system; as, the decimal scale; the binary scale, etc.

   4. (Mus.) The graduated series of all the tones, ascending or descending, from the keynote to its octave; -- called also the gamut. It may be repeated through any number of octaves. See Chromatic scale, Diatonic scale, Major scale, and Minor scale, under Chromatic, Diatonic, Major, and Minor.

3. Gradation; succession of ascending and descending steps and degrees; progressive series; scheme of comparative rank or order; as, a scale of being.

   There is a certain scale of duties . . . which for want of studying in right order, all the world is in confusion.
   --Milton.

4. Relative dimensions, without difference in proportion of parts; size or degree of the parts or components in any complex thing, compared with other like things; especially, the relative proportion of the linear dimensions of the parts of a drawing, map, model, etc., to the dimensions of the corresponding parts of the object that is represented; as, a map on a scale of an inch to a mile.

   Scale of chords, a graduated scale on which are given the lengths of the chords of arcs from 0[deg] to 90[deg] in a circle of given radius, -- used in measuring given angles and in plotting angles of given numbers of degrees.

A scale of chords may be used to set or read an angle 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 bisects the first arc. The line drawn from this point to the origin will be at the target angle.